Lymphocytes: precursor frequencies

The frequency of antigen‐specific cells will vary during development and in response to the first and subsequent encounters with an antigen, either through infection or immunisation, and is an important indicator of adaptive immune function. Antigen‐specific lymphocyte prevalence can be estimated indirectly and directly using several different techniques. Functional assays have been used for several decades to indirectly calculate the frequency of antigen‐specific lymphocytes by measuring a proliferative response, cytokine production or cytolytic activity in response to antigenic stimulation. The functional activity of individual lymphocytes is also able to be measured directly, which allows phenotypic analyses of antigen‐specific cells. More recently, labelled MHC (major histocompatibility complex)/peptide multimers have allowed researchers to directly enumerate and comprehensively phenotype lymphocytes using multiparameter flow cytometry.