Population Dynamics of CD4+ T Cells Lacking Thy-1 in Murine Retrovirus-Induced Immunodeficiency Syndrome (MAIDS)

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Abstract
Increased numbers of CD4+ Thy‐1 cells have been described in the spleen (SP) of mice with retrovirusinduced immunodeliciency (MAIDS). Since this phenotypic abnormality might have considerable functional importance, the expansion of the CD4+ Thy‐1 subset in MAIDS was characterized further. CD4+ Thy‐1− and Thy‐1+ T‐cell is from infected mice expressed similar densities of CD3 and TCR γ/β. In contrast, the Thy‐I− subset was uniformly CD44hi, even early in the disease when part of Thy‐I+ cells were still CD4410. The emergence of CD4+ Thy‐1−cells occurred first in SP and lymph nodes and was observed later in thymus. The important fraction ofCD4+ cells lacking Thy‐1 normally present in Peyer's patches was only weakly modified. Despite the major expansion of the CD4+ Thy‐1− phenotype. the proliferating fraction was not higher in this subset than in CD4+ Thy‐1+ cells from infeeted miee. Persistence after hydroxyurea administration was identical in both subsets, indicating similar mean cell lifespans. Taken together, these results show that the major expansion of CD4+ Thy‐I− T‐cells in MAIDS is not ascribable solely to increased proliferation within this subset. Phenotypic analysis suggests that CD4+ Thy‐I− cells result from the differentiation of Thy‐I+ cells induced by activation signals related to retroviral infection.