POPULATION-DYNAMICS OF CD4(-CELLS LACKING THY-1 IN MURINE RETROVIRUS-INDUCED IMMUNODEFICIENCY SYNDROME (MAIDS)() T)

Increased numbers of CD4(+) Thy-1(-) cells have been described in the spleen (SP) of mice with retrovirus-induced immunodeficiency (MAIDS). Since this phenotypic abnormality might have considerable functional i mportance, the expansion of the CD4(+) Thy-1(-) subset in MAIDS was ch aracterized further. CD4(+) Thy-1(-) and Thy-1(+) T-cells from infecte d mice expressed similar densities of CD3 and TCR alpha/beta. In contr ast, the Thy-1(-) subset was uniformly CD44(hi), even early in the dis ease when part of Thy-1(+) cells were still CD44(lo) The emergence of CD4(+) Thy-1(-) cells occurred first in SP and lymph nodes and was obs erved later in thymus. The important fraction of CD4(+) cells lacking Thy-1 normally present in Peyer's patches was only weakly modified. De spite the major expansion of the CD4(+) Thy-1(-) phenotype, the prolif erating fraction was not higher in this subset than in CD4(+) Thy-1(+) cells from infected mice. Persistence after hydroxyurea administratio n was identical in both subsets, indicating similar mean cell lifespan s. Taken together, these results show that the major expansion of CD4 Thy-1(-) T-cells in MAIDS is not ascribable solely to increased proli feration within this subset. Phenotypic analysis suggests that CD4(+) Thy-1(-) cells result from the differentiation of Thy-1(+) cells induc ed by activation signals related to retroviral infection.