Reference Database

The target antigen of the FN18 monoclonal antibody, called RhT3, is probably the rhesus monkey homologue of the human CD3 antigen, expressed on mature T cells. RhT3 appears to be polymorphic, since FN18 was not reactive with T cells from all the screened animals. Thus, immunofluorescent staining of peripheral blood lymphocytes with FN18 antibody revealed either a positive or a negative phenotype for the target antigen. In a rhesus monkey population, nonreactivity for FN18 was observed in low frequency (2.7%). Expression and non-expression of RhT3 appeared to be constant characteristics. Non-expression was not associated with any demonstrable immunodeficiency. Further, there seemed to be no association between the presence of the FN18 target antigen and sex, age or expression of MHC class I antigens. Family studies indicated that the positive phenotype is expressed in the same fashion by animals presumably heterozygous or homozygous for the positive allele, the negative phenotype being expressed only on cells from animals homozygous for an assumed blank allele. Therefore, the positive phenotype is likely to be transmitted in an autosomal dominant mode. In the animals with the negative phenotype, normal T-cell numbers were present, as was demonstrated by B- and T-cell specific monoclonal antibodies. Cytoplasmic staining of cytospun lymphocyte preparations with FN18 revealed that polymorphism was present at the intracellular level. Cell proliferation tests, using PWM and Con A as mitogens, showed the presence of apparently functional RhT3 cell surface molecules in FN18 non-reactive animals. Polymorphism is therefore assumed to be at the epitope level.