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

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 CD44^hi, 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.