|Kehrli Jr, Marcus|
Submitted to: Veterinary Immunology and Immunopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/29/2008
Publication Date: 1/15/2009
Citation: Kaushik, A.K., Kehrli Jr., M.E., Kurtz, A., Ng, S., Koti, M., Shojaei, F., Saini, S.S. 2009. Somatic Hypermutations and Isotype Restricted Exceptionally Long CDR3H Contribute to Antibody Diversification in Cattle. Veterinary Immunology and Immunopathology. 127(1-2):106-113. Interpretive Summary: Cattle die as a result of many diseases. The majority of these can be categorized into deaths due to pneumonia and diarrhea. Viral diseases, such as bovine viral diarrhea virus, are leading contributors to each of these death losses. Immunity against bovine viral diarrhea virus is dependent upon the immune system's production of T lymphocytes and B lymphocytes that help combat the virus in cattle. The research reported here identifies a molecular basis for how B lymphocytes (the body's cells that make antibodies) generate antibody diversity against the multitude of pathogens in the cow's environment. We utilized an animal with a specific genetic defect in their immune system to take advantage of the antibody diversity found in immune compromised animals that experience chronic and recurrent diseases. The main benefit of this work has been the demonstration of how cattle B lymphocytes produce antibodies with different specificities and that there are differences among cattle antibodies based on their subtype. A more complete understanding of the very basics of bovine immunology, as reported here, will eventually enable scientists to more rapidly and effectively develop vaccines against various diseases.
Technical Abstract: Antibody diversification in IgM and IgG antibodies was analyzed in an 18-month old bovine (Bos taurus) suffering from naturally occurring chronic and recurrent infections due to bovine leukocyte adhesion deficiency (BLAD) involving impaired leukocyte Beta-2 integrin (CD11a,b,c/CD18) expression in leukocytes. Twenty four VDJC(IgM) and 25 VDJC(IgG) recombinations from randomly constructed cDNA libraries, originating from peripheral blood lymphocytes, were examined for the variable-region structural characteristics in IgM and IgG antibody isotypes. These analyses suggest that: a. expression of exceptionally long CDR3H is isotype restricted to cattle IgM antibodies and it somatically mutates during the development of an immune response; b. unlike IgG antibodies, strongly acidic amino acids predominate in IgM antibodies leading to increased water solubility that is likely to reduce immunigenicity and enhance its biodistribution; c. somatic mutations contribute significantly to both IgM and IgG antibody diversification but have significant differences in the patterns of 'hot spot' occurrence in the VDJC(IgM) and VDJC(IgG) recombinations and, also, position dependant amino acid diversity; and d. transition nucleotide substitutions predominate over transversions in both VDJC(IgM) and VDJC(IgG) recombinations consistent with the evolutionary conservation of somatic mutation machinery. Overall, these studies suggest that both somatic mutations and exceptional CDR3H size generation contribute to IgM and IgG antibody diversification in cattle during the development of immune response to naturally occurring chronic and multiple microbial infections. Indeed, IgM antibodies with exceptionally long CDR3H, earlier noted in mitogen activated B cells, are stably expressed and demonstrate mutations during the course of an immune response to naturally occurring infections.