Equine T-lymphocyte MHC II expression: variation with age and subset.

This paper describes the characteristics of a monoclonal antibody (CVS10) that reacts with an equine leukocyte antigen. On the basis of tissue distribution and biochemical characteristics, this antigen is equine MHC II. The equine MHC II antigen was found on a large subset of T-lymphocytes in addition to all B-lymphocytes, as has been reported previously. In addition MHC II was found to be present on a large proportion of both the mutually exclusive equine T-lymphocyte subpopulations which express either the equine homologues of CD4, or CD8. In a study of changes in equine MHC II expression with age it was found that far fewer lymphocytes express MHC II in neonatal foals than in adult horses. An increase with age was demonstrated. This age related change in MHC II expression was shown to occur principally within the T-lymphocyte subpopulation. It is proposed that this change may be associated with the development of a memory T-lymphocyte population, and that MHC II expression may be a marker for memory T-lymphocytes.