Table of Contents
Cornish, K. and D.J. Siler. 1996. Hypoallergenic
guayule latex: research to commercialization. p. 327-335. In: J. Janick
(ed.), Progress in new crops. ASHS Press, Alexandria, VA.
Hypoallergenic Guayule Latex: Research to Commercialization
Katrina Cornish and Deborah J. Siler
- HISTORY OF GUAYULE COMMERCIALIZATION
- THE CHANGING MARKETPLACE
- Latex and Latex Products
- Latex Allergy (Type I, IgE-Mediated)
- Causes of Latex Allergy
- The Latex-Hypersensitive Population
- Latex Allergy Amelioration
- Latex Allergy Circumvention
- HYPOALLERGENIC GUAYULE LATEX
- Production of Hypoallergenic Guayule Latex
- Commercialization Position
A fresh look at guayule has led to the discovery and development of
hypoallergenic latex to supply a major, new market. Guayule (Parthenium
argentatum, Gray, Asteraceae), a new industrial crop candidate, is a desert
shrub native to the Chihuahuan desert of Texas and Mexico. It is the only
species other than Hevea (the Brazilian rubber tree, Hevea
brasiliensis Muell. Arg.) that has been used for rubber production on a
commercial scale. Guayule has been known to produce rubber for at least a
millennium, but modern commercialization efforts have been unsuccessful. The
resurgence of guayule research since the early 1970s has resulted in higher
yielding lines and improved agronomic practices, but the low price of imported
Hevea natural rubber from tropical countries has continued to bar
guayule rubber from the marketplace.
An extraordinary series of events has reversed guayule's dismal prospects,
culminating with the emergence of an important natural rubber market in which
Hevea cannot be used, i.e. hypoallergenic latex products. This
superb opportunity for guayule has arisen because Hevea latex products,
due to increased usage and manufacturing short-cuts, are causing serious and
widespread health problems. Proteins present in Hevea latex products
can trigger immediate (Type I) hypersensitivity, which in its most serious
manifestation, leads to life-threatening anaphylaxis. Synthetic alternatives
to many Hevea latex products do not have the required range of physical
properties that encompass resilience, strength, elasticity, and viral
impermeability. The unique properties of natural rubber, together with
concerns for public safety, make the development of an alternative,
hypoallergenic source of natural rubber imperative. Guayule makes high quality
rubber which can be produced as a latex suitable for hypoallergenic product
manufacture. Guayule latex products should be safe for use by even those with
severe Type I latex allergy. Hypoallergenic latex presents a high margin,
rapidly-expanding market for guayule rubber latex products. This market
provides a sufficient premium to permit the immediate development of guayule as
a major domestic crop. Large scale trials have produced low protein,
hypoallergenic guayule latex, which we have shown suitable for product
Natural rubber is a vital raw material used in enormous quantities by
commercial, medical, transportation, and defense industries. The United States
is wholly dependent upon imports from developing countries. Although over
2,500 plants are known to produce natural rubber, few synthesize commercial
quality or quantities. At present, all commercial natural rubber comes from a
single, tropical, plant species, Hevea brasiliensis, largely from
plantation-grown, bud-grafted, clonal material. Continuity of the natural
rubber supply is endangered by many factors, including diminishing acreage (as
growers switch to more profitable crops, such as palm oil), increasing global
demand, changing political climes, and crop disease. The recent widespread
occurrence of life-threatening "latex allergy" to Hevea rubber products
makes development of an alternative source of natural rubber imperative. A
domestic natural rubber crop would guarantee sufficient natural rubber to
supply existing United States strategic demands as well as the new, major,
health-related, hypoallergenic rubber market. A sustainable, domestic rubber
industrial crop also would enhance rural economies, utilize semi-arid lands,
and bring retired farmlands back into profitable production.
In any development of a new crop, however worthy the underlying rationale, the
new crop must have an existing market and be profitable for the grower and the
buyer. Approaches to achieving commercial competitiveness may be grouped in
two categories, (1) increasing the yield and (2) adding value to the
agricultural commodity. Both of these approaches have been attempted with
Guayule commercialization has been ventured at several different times during
the twentieth century (as reviewed by Bonner 1991), but without lasting
success. In the 1900s, the Continental Mexican Rubber Company harvested and
processed the native guayule stands. At the height of this endeavor (1910),
rubber production was 10,000 t/year and constituted 24% of U.S. rubber imports.
From 1906 to 1912, the United States imported 42,000 t of guayule rubber from
Mexico. Production ended due to depletion of the native stands and civil
unrest. A fresh enterprise began in Texas with the appearance of the
Intercontinental Rubber Company and the cultivation of guayule. Rubber
production reached 1,400 t/year, with commercial plantings of over 7,500 acres,
but ended in 1929 with the onset of the Great Depression. Guayule then had to
await the Second World War and the United States inauguration of the Emergency
Rubber Project to supply the strategic raw material in light of the war-induced
dearth of Hevea natural rubber supplies. This enormous undertaking
employed 1,000 scientists and technicians, 9,000 laborers and 13,000 ha of
guayule under cultivation in three States. The project had produced its first
1,400 t of rubber when the war ended. The guayule plantings were destroyed due
to the reavailability of Hevea rubber, a perhaps over-optimistic view of
the utility of synthetic rubber, and international political pressure.
Guayule then waited until the oil shortage of the 1970s. High oil prices
caused increased costs of synthetic rubber and led to renewed interest in
guayule as an alternative source of natural rubber. Scientific conferences
took place which led to extensive lobbying and, in 1978, the Native Latex
Commercialization and Economic Development Act (PL 95-592) (Huang 1991). The
Gila River Indian Community Guayule Project got underway in 1981, and 1984 saw
the act reauthorized as the Critical Agricultural Materials Act (PL 98-284).
Considerable progress was made in improving guayule's commercial viability
through plant breeding and agronomy. As has been described in detail (Ray
1991), rubber yields were between 220 and 560 kg/ha during the 1950's, and by
the Second Guayule Regional Variety Trials (1985-1988) annual yields had been
increased to between 600 and 900 kg/ha (Thompson and Ray 1989). Yields of over
1,100 kg/ha have been achieved in breeding plots (Gathman et al. 1989). The
advanced lines also have been selected for their ability to regrow after
pollarding (trimming the shrubs to about 10 cm above soil level, leaving the
trunk and branch stubs). First harvest by pollarding at three years, followed
by regrowth and reharvest at two year intervals maximizes the profitability of
the current best lines (Thompson and Ray 1989; Estilai and Ray 1991). The
affect of cultural practices on rubber yield has been extensively reviewed
(Thompson and Ray 1989; Foster and Moore 1991; Nakayama 1991) and suitable
agricultural machinery for modern mechanized farming has been successfully
developed (Coates 1991). Direct seeding methodologies also have been developed
(Foster and Moore 1992; Foster et al. 1993) which greatly reduce the costs
involved in the transplanting procedures previously required for good stand
establishment. Of course, growing guayule in areas climatically unsuitable for
its cold-induced rubber biosynthetic pathway (Appleton and van Staden 1989; Ji
et al. 1993; Cornish and Siler 1996) will not give acceptable rubber yields.
During this research and development period, the Gila River Indian Community
Guayule Project planted 117 ha of guayule (1981 to 1986) predominantly of line
Gila-1 (or AZ101). Unfortunately, this line proved to be a hybrid between
P. argentatum and the large, but virtually rubber-free, P.
tomentosum. Unsurprisingly, the hybrid proved to be a rapidly-growing but
low-yielding line. Nonetheless, a processing plant based on a continuous
simultaneous solvent extraction and rubber fractionation process, was built on
the Gila River Indian Reservation (Wagner and Schloman 1991). The guayule
rubber produced was manufactured into airplane and truck tires. Performance
testing has shown that guayule rubber truck tires are of comparable quality to
Hevea rubber tires (pers. commun. Wayne Lucas, Automotive Systems
Engineering Branch, Yuma Proving Grounds).
This commercialization effort targeted the production of natural rubber in
competition with imported Hevea bulk rubber, essentially for the tire
market. Thus, guayule was confined to competition with the cheapest end of the
natural rubber market. The profitably increases achieved through plant
breeding and improved cultural practices were not sufficient to support
commercialization. Approximately a doubling of yield or price was still
required (Wright et al. 1991).
The value of an agricultural commodity may be increased through the discovery
of a specific new use or market, or through increased demand and/or decreased
supply leading to lower competition. The global demand for natural rubber is
on the increase (Reisch 1995) even though area has declined, resulting in
substantial price rises. Also, latex rubber is more expensive than bulk
(solid) rubber, which costs usually about 70% the latex price. Guayule has
been extensively investigated (Whitworth and Whitehead 1991) with the hope of
its commercialization as a true competitor in natural rubber markets currently
occupied by Hevea bulk rubber (d'Auzac et al. 1989). As mentioned
earlier, guayule rubber has been used for fabricating automobile tires (Hammond
and Polhamus 1965; pers. commun. Wayne Lucas) but has not been used for dipped
or extruded goods since their manufacture requires the raw rubber to be in
latex form. Unlike laticiferous species, such as Hevea, guayule
produces rubber in individual cells, located predominantly in the root and stem
bark parenchyma. None of the established extraction methods used to produce
bulk rubber from guayule, whether solvent or water-based (Whitworth and
Whitehead 1991), have led to competitively-priced product, even from the best
bred lines. Guayule, as a source of more valuable latex rubber, has much
greater commercial potential than bulk rubber.
Natural rubber is used in over 40,000 different products, including more than
300 medical applications. High-value dipped and extruded products are
manufactured directly from the Hevea latex. A life-threatening "latex
allergy" has developed, in recent years, that is triggered by proteins present
in latex. Synthetic alternatives to Hevea latex products do not have
the required range of physical properties that encompass resilience, strength,
elasticity, and viral impermeability. The unique properties of natural rubber,
together with concerns for public safety, make the need for an alternative,
hypoallergenic source of natural rubber imperative. This special need creates
an excellent opportunity for the development of a new, hypoallergenic, natural
In this section, we review the feasibility of ameliorating and circumventing
Type I latex allergy caused by the presence of Hevea proteins in latex
products. Also, we report on the development of hypoallergenic guayule latex.
Latex products had been safely used for many decades with only infrequent
contact reactions (Type IV) occurring generally in response to chemical
additives. However, in the 1980s, life-threatening Type I allergy appeared,
which is triggered by proteins present in Hevea latex. A hypersensitive
individual must take care to avoid contact with all natural rubber products
made from Hevea latex. Allergic reactions to Hevea rubber
products include local urticaria, systemic urticaria, rhinitis, conjunctivitis,
edema, bronchospasm, tachycardia, anaphylaxis, and death (Slater 1989; Slater
et al. 1990; Morales et al. 1989; Tomazic et al. 1992). The Food and Drug
Administration responded to this public health problem by issuing a medical
alert (March 1991) concerning use of latex products. Most, but not all, severe
reactions occur from direct patient contact with latex gloves and other devices
during medical and dental procedures.
The surge of Type I latex allergy coincided with sudden world-wide increased
demand for latex gloves in response to institution of universal precautions to
prevent transmission of the human diseases caused by HIV and Hepatitis B. New
and inexperienced glove manufacturers entered the market, and short-cuts in
manufacturing became common, in order to supply the increased demand (Bodycoat
1993). Over-production of these gloves led to a drop in price which, combined
with the increasing demand, induced some other manufacturers to reduce costs
through curtailed processing (Russell-Fell 1993). Altered manufacturing
processes included reduction and sometimes elimination of the leaching step
normally used to wash the latex products (Bodycoat 1993; Russell-Fell 1993).
The washing process removes soluble latex components, as well as chemical
additives, and underwashed products contain high levels of Hevea latex
The use of high protein latex products, especially of single-use latex gloves,
as well as their extensive deployment throughout society, led to widespread
development of Type I latex allergy. The problem was compounded by
requirements for health-care workers to frequently change gloves. Proteins in
gloves can bind to glove powder. When gloves are removed, the powder becomes a
source of air-borne, respirable, latex allergens (Tarlo et al. 1994; Tomazic et
The first incidents of latex allergy, in the United States, were reported in
1988. Numbers had increased to at least 500,000 by 1992. Published estimates,
based on medical testing, indicate that 17,000,000 adults in the general U.S.
population are affected by Type I latex allergy, 10%-40% of health care
workers, and up to 60% of multiple surgery cases including spina bifida
children (Alenius et al. 1993; Hamann 1993; Ownby et al. 1994). Many other
countries around the world also have serious problems with latex allergy. The
number of latex-hypersensitive people continues to climb due both to increased
usage of latex products and to the continued sale of high protein latex gloves
and other products. Manufacturing methods known to reduce product protein
levels are available, but it is important to realize that even the best
processing practices currently available will not produce latex products that
Since Type I latex allergy arose because of high protein latex products, the
manufacture and use of low protein latex products should greatly diminish the
incidence of new allergy cases. Various methods for removing protein from
latex and latex products are available (Pailhories 1993). However, future
latex products will have to be shown to be low protein.
Hevea latex and latex products are difficult materials to assay for
protein since latex is a cytoplasm that also contains about 30% rubber in the
form of microscopic particles. Latex proteins fall into several groups with
some soluble (48%), some associated with organelles (26%), and some bound to
the surface of rubber particles (26%) (Kekwick 1993). Allergic patients can
react to a large number of different latex protein allergens, which can
originate from all of these protein groups. At least 57 different latex
proteins and peptides, out of approximately 240, have been shown to be human
allergens (Alenius et al. 1994). These range in size from 2 to 100 kD (Hamann
1993; Yeang et al. 1996). Nevertheless, soluble latex proteins, and others not
directly associated with rubber particles, should be easier to remove from
latex and/or latex products than the rubber particle-bound proteins (Siler and
Cornish 1992). Their removal would substantially lower the overall protein
level, thus reducing the allergenicity of the final latex product for people
who have not yet developed latex allergy.
Latex protein assays must effectively measure all classes of protein allergens
in latex, or latex products, and eliminate interference from nonproteinaceous
substances in the latex and additives such as ammonia. A suitable method for
assaying protein levels in latex has been developed (Siler and Cornish 1995)
and an ASTM panel has developed an assay for use with latex products (ASTM
As discussed above, it is possible to produce low protein latex products that
should moderate the incidence of new allergy cases. However, trace amounts of
allergen can induce serious systemic reactions in a hypersensitive person.
Thus, production of latex products safe for use by allergic individuals
requires the elimination of all latex allergens.
Allergens that are not associated with the rubber particles can be removed from
the latex, prior to product manufacture, by repeated purification cycles using
centrifugation/flotation (Siler and Cornish 1994a). Certain types of dipped
products, such as some surgical gloves, electricians' gloves, and condoms, are
made from doubly-centrifuged latex. This is produced by centrifuging standard
latex (30%-35% dry rubber), diluting to 20%-25% with water, and centrifuging
again. This process can remove about 70% of the non-rubber substances
(Pailhories 1993). However, 25% of the proteins are bound to the rubber
particles. Even extensive rubber particle purification does not remove them
and these proteins would persist in the final product.
We tested the immunogenicity of various latex materials using antibodies,
raised in rabbits, against proteins extracted from Hevea latex films.
These Hevea latex protein antibodies recognized many of the proteins in
complete Hevea latex (Siler and Cornish 1994b). As expected, purified
rubber particle preparations, from which the soluble latex proteins were
removed, contained far fewer proteins than latex (Siler and Cornish 1992,
1994b). Nevertheless, these highly purified Hevea rubber particle
preparations still contained numerous proteins many of which are immunogens
(Siler and Cornish 1994b). Also, a report that IgE antibodies from serum of
latex-sensitized individuals recognized the 14.6 kD protein "rubber elongation
factor" implicates this abundant rubber particle-bound protein as a major
allergen in Hevea latex (Czuppon et al. 1993).
Thus, complete removal of both rubber particle-bound and soluble latex protein
allergens is required to produce a Hevea latex material safe for use by
a latex-hypersensitive person. Removal of the rubber particle-bound proteins
would necessitate drastic treatment e.g. with proteases and/or detergents, that
would not only probably be prohibitively expensive, but also likely would
adversely affect the performance characteristics and quality of the resulting
Some manufacturers have introduced so-called "hypoallergenic" Hevea
latex gloves into the market. Although some of these gloves are low
protein, tests demonstrated that many contain substantial amounts of proteins
that bind IgE antibodies from sera of Hevea-hypersensitive patients
(Yunginger et al. 1994). Low protein hypoallergenic gloves would be unlikely
to induce allergies in individuals not already allergic to Hevea latex
proteins. However, these gloves would not be safe for use by people who
are already Hevea-hypersensitive.
Suggestions have been made to remove the allergens from Hevea latex by
breeding or by using genetic engineering techniques (antisense technology) to
eliminate the allergenic proteins. These approaches are biologically unsound.
This is primarily because many different latex proteins have been shown to be
allergens (see above). It is very unlikely that they could be removed from the
Hevea tree without dire effects on latex production and plant health.
Furthermore, the genetic base of cultivated Hevea is extremely narrow
which would likely preclude a plant breeding approach. We confirmed that
clonal selection is unlikely to eliminate latex antigens in experiments that
demonstrated that Hevea latex protein antibodies recognized many
proteins in samples from three different commercial lines of Hevea
(Siler and Cornish 1994b). The proteins recognized by the antibodies
showed similar patterns in all three clones.
Different rubber-producing species may contain proteins distinct from those of
Hevea and perhaps provide a source of hypoallergenic rubber (Siler and
Cornish 1992). Guayule rubber is of high molecular weight and of comparable
quality to Hevea rubber. However, guayule had not been seriously
considered as a source of latex rubber (this liquid rubber form is essential
for the manufacture of dipped and extruded products) since it does not produce
its rubber as a tapable latex. Unlike the laticiferous species Hevea,
guayule rubber particles are compartmentalized in individual bark parenchyma
cells. Nonetheless, methods have been developed to extract guayule rubber in a
latex-like form (Jones 1948; Madhavan and Benedict 1984; Cornish and Backhaus
1989; Cornish 1993). It seemed likely that the Hevea protein allergens
would be absent from guayule latex since the Hevea and guayule are
evolutionarily-divergent species and their rubber particle protein complements
are dissimilar. We have proven this to be true. Anti-Hevea latex
protein antibodies did not recognize latex proteins from guayule using ELISA
(enzyme-linked immunosorbent assay). Proteins extracted from purified rubber
particle preparations of guayule showed no reaction, even at concentrations at
least 2 or 3 orders of magnitude above the Hevea rubber particle protein
concentration that elicited a positive reaction (Siler and Cornish 1994b).
Western blot analyses of the rubber particle proteins from guayule with the
Hevea antibodies confirmed the lack of cross-reactivity (Siler and
Cornish 1994b). These results indicate that Hevea latex allergy can
indeed be circumvented using rubber from guayule.
Our results were confirmed in preliminary clinical trials on humans. In one
trial, individuals with proven hypersensitivity to Hevea latex were
skin-prick tested with latex samples from different sources. All these
subjects reacted strongly to Hevea latex (wheals and flare), whereas
none responded to guayule latex (Carey et al. 1995). In a second trial, 56 "at
risk" people (such as health care workers, spina bifida patients, and multiple
surgery cases), ages 16 months to 72 years, and three controls, were tested
both by skin prick and by in vitro RAST (radioallergosorbent assay) assays (Ber
et al. 1993). The RAST assay detects the presence of human IgE antibodies
specific to Hevea latex proteins. 25 reacted to Hevea materials,
25 reacted in the skin prick test, and 30 in the RAST. None reacted to guayule
latex, confirming the earlier clinical test results, and our experiments using
the rabbit anti-Hevea latex protein antibodies.
Guayule rubber latex should be suitable for the manufacture of high quality,
hypoallergenic natural rubber products safe even for the
Hevea-hypersensitive individual. Some other rubber-producing plant
species also produce high molecular weight rubber but currently none are
suitable for commercial cultivation. In contrast, guayule agronomics are well
understood (see History of Guayule Commercialization above).
Thus, diverse immunological tests have demonstrated that guayule latex is truly
hypoallergenic and that guayule latex products could be used safely by Hevea
latex-sensitive people. Of course, it is essential that guayule latex
products be maintained as low protein so that allergy problems don't redevelop
later. The most difficult proteins to completely remove are those bound to the
rubber particles themselves. Guayule rubber particles have less protein than
Hevea (Cornish et al. 1993) and, therefore, guayule latex could be
produced with lower protein levels than will ever be possible with Hevea
We have developed processing methods to extract intact guayule rubber particles
and generate an artificially-produced purified latex (Cornish 1993). These
methods also are suitable for the production of latex from other rubber
Guayule hypoallergenic latex presents a major new, high value, rapidly
expanding market because hypersensitive people cannot safely use Hevea
latex products. The U.S. market for latex gloves alone had a retail value of
over $3,000,000,000 in 1993. Hypoallergenic natural rubber latex products
would provide a sufficient premium to permit the immediate development of
guayule as a new crop even at its current rubber yield (about 10% on a dry
During the Spring of 1994, a production run was carried out in Arizona, where
2,300 kg of field-grown guayule shrub were processed. A processing system was
constructed and used (Coates and Cornish, unpublished results) to generate
ammoniated guayule latex for allergy testing, performance testing, and
manufacturing trials. This batch of guayule latex was less highly purified
than the latex used in the allergy trials described in the last section.
Nevertheless, immunological experiments (RAST and Western blot analysis) to
investigate the ability of IgE antibodies from Hevea latex allergic
patients, and IgG antibodies from hyperimmunized mice, to detect proteins in
the guayule latex displayed a total lack of cross-reactivity (Siler et al.
1996). Several additional trials have been completed on this material
demonstrating that guayule latex (1) may be compounded using similar procedures
to Hevea latex (Schloman et al. 1996), (2) can be used to produce
quality latex medical products (H.F. Bader, and K. Cornish, unpublished data),
and (3) prototype dipped films provide an impermeable barrier to virus
transmission (D. Lytle and K. Cornish, unpublished data).
Hypoallergenic latex reflects a technological breakthrough that provides a new
impetus to the commercialization of this new crop. However, guayule latex
would be years away from successful commercialization but for the diverse and
numerous successes of the scientists involved in guayule research in recent
years, as described earlier. Their work has led to the advanced guayule lines
and refined, mechanized agronomic practices which provide an essential
foundation for guayule latex commercialization.
Large-scale production of guayule latex is feasible and the high quality of
guayule natural rubber makes it suitable for hypoallergenic product
manufacture. These products should be safe for use by the
Hevea-hypersensitive population. Clinical trials on humans showed that
even severely Hevea-hypersensitive patients had no reaction to guayule
latex. Guayule latex products must be produced with low protein levels so that
allergy problems don't develop with the new material. Guayule rubber particles
have much less protein than those of Hevea, and guayule latex can be
produced with lower protein levels than even highly purified Hevea
latex. Upon the generation of sufficient supplies, hypoallergenic guayule
latex products first would become available to hypersensitive patients, and the
at-risk health-care profession, and then to the general population. Guayule
latex provides the first, natural rubber solution to the urgent global need for
a reliable hypoallergenic source of natural rubber latex. Concerted and
dedicated efforts should make safe guayule latex products a reality and the
guayule crop a major feature of the farming landscape of the south-western
United States. Continuing research also should lead to the introduction of
genetically-engineered guayule lines with enhanced rubber yield and extended
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Last update June 13, 1997