CD45RO expression on bovine T cells: relation to biological function.
Bembridge GP., MacHugh ND., McKeever D., Awino E., Sopp P., Collins RA., Gelder KI., Howard CJ.
The 180,000 MW isoform of CD45 (CD45RO) has been identified in cattle with a novel monoclonal antibody (mAb) (IL-A116). This has allowed a more precise analysis of T-cell function in relation to CD45 isoform expression. Within the CD4+ and CD8+ T-cell populations, CD45RO+ and CD45RO- subsets were evident. Most CD4+ and CD8+ T cells that expressed the CD45RO isoform did not express the 220,000 and 205,000 MW isoforms recognized by mAb CC76. In contrast, the WC1+, CD2-, CD4-, CD8-, gamma delta T-cell receptor (TCR)+ T cells in bovine peripheral blood mononuclear cells (PBMC) were all CD45RO+. Monocytes and granulocytes were CD45RO+ but B cells were CD45RO-. Sorting experiments with CD4+ T cells from an immunized calf demonstrated that proliferative responses to ovalbumin (OVA) were entirely within the CD45RO+ subset. Following stimulation with concanavalin A (Con A) the CD45RO- subset of CD4+ T cells produced transcripts for interleukin-2 (IL-2) but not IL-4 or interferon-gamma (IFN-gamma), while the CD45RO+ subset produced mRNA for IL-2, IL-4 and IFN-gamma. Biologically active IL-2 was present in supernatants from both CD45RO+ and CD45RO-, CD4+ T cells, and IFN-gamma protein was identified by ELISA in supernatants from the CD45RO+ subset, confirming the production of cytokines implied by polymerase chain reaction (PCR). In contrast, sorting experiments with CD8+ T cells from animals immune to the protozoan parasite Theileria parva revealed substantial numbers of cytotoxic T-lymphocyte precursors in both the CD45RO+ and CD45RO- subsets. Thus it appears that although all antigenically primed CD4+ T cells remain CD45RO+, and expression of this molecule consequently identifies memory cells within PBMC, antigenically primed CD8+ T cells down-regulate CD45RO expression after activation.