According to a 2004 study in the
Journal of Allergy and Clinical Immunology, seafood allergies are reportedly present in 2.3% of the general population, or approximately
6.6 million Americans (Sicherer, Munoz-Furlong, and Sampson, 2004). This represents a serious
health concern for the U.S. With seafood
– notably shellfish – consumption having risen in popularity and frequency globally,
it has become pertinent that shellfish allergies become better characterized
(NOAA, 2013).
The manifestation of shellfish allergies can be highly
variable with symptoms ranging from hives, tingling
or swelling of the lips, tongue or throat, chest tightness, shortness of breath or difficulty
breathing, nausea and vomiting, to full-blown anaphylaxis (Cleveland Clinic,2012). The allergens associated with shellfish allergies are not well
characterized and thus management of such an allergy is often simply limited to
avoidance or dietary elimination of shellfish. Additionally,
treatment is restricted to emergency care following exposure (Lieberman et al.,2010). So far, it is known that there are heat stable antigens within shellfish
that bind to human IgE, an immunoglobulin or antibody that likely originally evolved
as a defense against internal parasites such as helminthes and now
significantly contributes to immune-mediated hypersensitivity reactions. Once
bound to an allergen, IgE initiates intracellular signaling, leading to the degranulation
of immune cells. Degranulation is the release of antimicrobial cytotoxic molecules
and mediators of inflammation, which in this case eventually leads to the
previously described symptoms. One major type of shrimp allergen that has been
identified is tropomyosin, a protein associated with the thin filaments in
muscle cells and microfilaments in non-muscle cells. However, there are many other
IgE reactive shellfish proteins that have yet to be identified
A recent study published in PLOS One sought to identify and study different IgE-reactive components of commonly
eaten shellfish. The investigators
primarily sought to compare the IgE reactivity of raw and heated proteins of
the blue swimmer crab and the black tiger prawn. By treating whole blood and blood
sera of individuals with and without shellfish allergies with raw and cooked
shellfish extracts, investigators were able to quantifiably measure the degree
to which IgE reactivity occurred in response to treatment and to identify
unique IgE reactive proteins.
What was found was that cooked
shellfish extracts were much more IgE reactive than raw extracts. It is possible that this higher level of
reactivity is a result of people being more likely to have previously consumed
cooked crab or prawn and that their immune systems were more compromised when
exposed to these heat modified proteins. Additionally, it was found that another type
of tropomyosin, the crab protein Por p 1, triggers IgE reactions in a similar manner
to the black prawn tropomyosin, rPen m 1. A sequence analysis of both proteins showed
that they bore a strong genetic homology to one another. Such homology might allow for
cross-reactivity, or the sensitization of an individual to one protein which
allows them to have an effector reaction to the other similar protein on a separate
occasion.
What this study shows is that some
shellfish allergies can be preserved across shellfish species as a result of
the presence of homologous IgE reactive proteins. Additionally, heat treating blue swimmer crab
proteins can lead to a marked increase in IgE reactivity. This research provides a basis for future
studies, as well as for shellfish allergy management and diagnosis, by better
characterizing shellfish allergens and outlining factors that may contribute to
more robust allergic reactions.
Helpful Links
To learn more about shellfish allergies, see: http://www.mayoclinic.com/health/shellfish-allergy/DS00987
To learn more about IgE and its role in allergic
inflammation, see: http://www.worldallergy.org/professional/allergic_diseases_center/ige/
Primary Source
Abramovitch, J.B., Kamath S., Varese, N., Zubrinich C.,
Lopata, A.L., O’Hehir, R.E., Rolland, J.M. (2013) IgE reactivity of blueswimmer crab (Portunus pelagicus)Tropomyosin, Por p1, and other allergens; Cross-reactivity with black tigerprawn and effects of heating. PLOS One
8:1-13.
Secondary Sources
Sicherer, S.H., Munoz-Furlong A., Sampson H.A. (2004)Prevalence of seafood allergy in the United States determined by a randomtelephone survey. J Allergy Clin Immunol
114:159-165.
Cleveland Clinic. (2012) Shellfish allergies. Health Hub
from Cleveland Clinic. Accessed at http://my.clevelandclinic.org/disorders/shellfish_allergies/hic_shellfish_allergies.aspx
on 20 December 2013.
Lieberman, P., Nicklas R.A., Oppenheimer J., Kemp S.F., Lang
D.M.(2010) The diagnosis and management of anaphylaxis practice parameter:2010. Update. J Allergy Clin Immunol 126:477-480.
Image Source
Original Image from: http://paleospirit.com/wp-content/uploads/2012/06/Blue_crab.jpg
No comments:
Post a Comment