Latex allergy has been recognized in Europe for over ten years, and
only relatively recently in the U.S. The allergic reactions such as rhinitis, asthma or anaphylactic shock are caused by constituent proteins of
rubber latex, some of which are retained in finished latex products.
Recent studies have demonstrated that latex sensitive patients can be
sensitive to different proteins in latex with great variability of the individual immune response.
Recently, it has been suggested that the allergenicity of the latex
devices is related to the total protein content, and various treatments
have been suggested to reduce the protein content, such as centrifugation, leaching, chlorination, and enzyme hydrolysis. However, as
known from other allergen extract preparations, not all proteins are
allergens. Therefore, the measurement of total protein content does not
necessarily correlate with the allergenicity of the sample.
To confirm the clinically relevant allergenic activity of a preparation,
in vivo methods such as skin testing or provocation test are necessary.
Unfortunately, this is not always possible. Therefore, various in vitro
tests have been developed in which human allergic or IgE antibodies
against latex proteins are used to confirm the presence of the
allergenic proteins.
TOTAL ALLERGENIC ACTIVITY
The in vitro method most often used to measure total allergenic activity is the RAST (radio allergosorbent test) inhibition. This test
measures the capacity of allergies to inhibit the binding of human anti-
bodies to corresponding allergens. For reliable results, solid phase
allergens and human IgE sera must be properly selected. All allergens
must be present on the solid phase and IgE antibodies against all allergens in the sample and solid phase must be included in the serum pool.
All the allergens from raw latex are not necessarily present in latex end
products, and end products may also contain allergens different from
raw latex as a result of rubber processing. Since patients respond heterogeneously to numerous latex allergens, multiple latex RAST-
positive sera should be included in the tested serum pool.
INDIVIDUAL ALLERGENS
Individual allergens in natural rubber latex can be characterized by a
specific and sensitive immunologic test known as IgE immunoblotting,
in which the latex proteins are separated according to their molecular
weight or isoelectric point. It is notable that in some of these methods,
samples are not in their native forms, but have been altered by treat-
ment with chemicals or heat. As a result, proteins consisting of several
subunits are split into their smaller forms, which may have an effect on
their capacity to bind IgE sensitizing latex allergen molecules.
OTHER METHODS
Animal IgG antibodies, produced by immunization of rabbits using
latex antigens, can be used in various electrophoretic methods as a precipitation agent. Because of the heterogeneous IgG response, sera from
more than one immunized animal must be used. The specificity of the
animal antibody depends on the immunizing protein used and the
immunization procedure. The immunizing agent should contain all
potential allergens from raw latex and end products. The proteins,
which react with animal IgG antibodies are called antigens, but they
are not necessarily allergens, unless they bind human IgE antibodies.
Another in vitro test to measure allergen activity is the histamine test.
This test measures the capacity of latex to release histamine from
human basophils. However, this mechanism is not always IgE
mediated and does not necessarily describe allergenic activity. In
addition, fresh sera from latex allergic patients and control subjects
are needed for each analysis.
Thus, there are numerous ways in which pertinent latex antigens and
allergens may be evaluated. Such an evaluation should help identify
sensitized patients as well as sensitizing products.
