Elevated production of interferon‐γ and interleukin 4 by mature T cells from autoimmune Ipr mice correlates with Pgp‐1 (CD44) expression

The cell surface glycoprotein, Pgp-1 (CD44), has been shown to be a marker of murine memory T lymphocytes. When activated, Pgp-1hi memory T cells produce strikingly higher amounts of interferon-gamma (IFN-gamma) than naive Pgp-1lo T cells, yet both subsets make similar levels of interleukin (IL)2. Whereas Pgp-1hi cells represent only 20%-25% of peripheral T cells from most strains, this marker is expressed by the vast majority (greater than 90%) of T cells from autoimmune MRL mice homozygous for the lymphoproliferation (lpr) gene. The massive lymphadenopathy that develops in lpr/lpr mice is composed of both non-mature (CD4-CD8-) T cells as well as a greatly expanded number (up to 300-fold) of mature (CD4+CD8-,CD4-CD8+) T cells. Paralleling the expression of high levels of Pgp-1, we find that compared to normal mouse T cells, the lpr mature T lymphocyte subsets are also very high producers on a per cell basis of IFN-gamma and, for the CD4+ subset, IL 4. Increased concentrations of IFN-gamma and IL 4 produced by large numbers of lpr Pgp-1hi mature T cells could contribute to the autoimmune syndrome in MRL lpr/lpr mice through the effects of these cytokines on augmenting MHC class II expression and production of certain classes of antibodies.