Mice homozygous for lpr and gld develop profound lymphadenopathy characterized by the expansion of two unusual T cell subsets, a predominant Ly-5(B220)+ CD4- CD8- double negative (DN) population and a minor CD4 dull+ Ly-5(B220)+ population. The mechanisms promoting lymphoproliferation are unknown, but one possibility is a abnormality in the production of cytokines that regulate T cell growth. In the present report, unfractionated LN cells and sorted T cell subsets from C3H-lpr, -gld, and -+/+ mice were compared for spontaneous and induced secretion of a spectrum of lymphokines. In addition, CD4+, CD4 dull+ Ly-5(B220)+, and DN T cells were examined for expression of CD3 epsilon, TCR-alpha/beta heterodimers, Ly-6C, and CD44 and for proliferative responses to immobilized anti-TCR mAb and cofactors. These studies revealed that sorted DN T cells did not secrete IL-3, IL-4, IL-5, IL-6, GM-CSF, TNF-alpha, or IFN-gamma spontaneously or after TCR-alpha/beta cross-linking. In contrast, stimulated unfractionated lpr and gld LN cells proliferated strongly and secreted high levels of IFN-gamma and TNF-alpha and low levels of IL-3, IL-4, and IL-6. Despite a 5- to 10-fold deficit in the frequency of CD4+ and CD8+ T cells, cytokine secretion by lpr and gld LN generally exceeded that of +/+ LN. Comparisons of cytokine secretion by stimulated CD4+ T cells revealed that +/+, lpr, and gld CD4+ Ly-5(B220)- T cells proliferated strongly, but only lpr and gld cells produced significant levels of IFN-gamma. The lpr and gld CD4+ T cells also produced higher levels of TNF-alpha and IL-2 than +/+ cells. In contrast to normal CD4+ T cells, lpr and gld CD4+ Ly-5(B220)+ T cells proliferated weakly and did not secrete TNF-alpha, IL-2, or, in most experiments, IFN-gamma after stimulation. Phenotypic studies of T cell subsets revealed that unstimulated lpr and gld CD4+ Ly-5(B220)- T cells express significantly higher levels of CD44 than +/+ CD4+ T cells. In addition, CD4 dull+ Ly-5(B220)+ cells closely resembled DN T cells in size and expression of TCR-alpha/beta, CD3epsilon, CD44, and Ly-6C. Since elevated CD44 expression is generally associated with T cell activation and only previously activated normal CD4+ T cells produce high levels of IFN-gamma in vitro, our data suggest that lpr and gld CD4+ Ly-5(B220)- T cells contain a higher than normal proportion of primed or memory T cells and thus may be polyclonally activated in vivo.(ABSTRACT TRUNCATED AT 400 WORDS)

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