The CD45RB-associated epitope defined by monoclonal antibody CZ-1 is an activation and memory marker for mouse CD4 T cells.

Monoclonal antibody CZ-1 defines a novel sialic acid-dependent CD45RB-associated epitope. The CZ-1 antigen is expressed on the subpopulation of CD4 T cells that proliferate in response to IL-2. Because IL-2 responsiveness often denotes T cell activation, we examined the expression of the CZ-1 antigen on CD4 T cells taken from mice at various times during an infection with lymphocytic choriomeningitis virus (LCMV). The blast-sized CD4 T cells at Day 6 postinfection were CZ-1+. Further cell surface phenotyping showed that those blast cells activated at Day 6 postinfection were CD45RBdimPgp-1brightMEL-14-. This contrasts with the CZ-1-CD45RBbrightPgp-1bright/dimMEL-14+ resting cell population prior to infection. To determine if memory CD4 T cells continued to express the CZ-1 epitope long after resolution of the LCMV infection, CD4+CZ-1+ and CD4+CZ-1- populations were purified by cell sorting and placed in an in vitro proliferation assay with LCMV-infected antigen-presenting cells. It was found that the CD4+CZ-1+ population contained virtually all of the virus-specific memory. The CZ-1 epitope is therefore both an activation and a memory marker for murine CD4 T cells.