Formation of antigen specific foci as a complement independent assay for individual antibody-secreting cells.

Antibody-forming cells (AFC) could be demonstrated by the binding of antigen to secreted antibody localized around the AFC. Using sheep red blood cells (SRBC) as antigen, this antigen binding was detected as foci of erythrocytes surrounding individual lymphocytes. Focus formation was antigen specific and involved the active secretion of antibody. AFC specific for antigens resistant to lysis, such as human red blood cells were also demonstrable with this assay. The focus assay provides a complement independent method for enumerating antibody-forming cells.