Antigen-specific t-cell activations distinguished by in vivo anti-CD4 antibody treatment

This study identifies activation characteristics of PPD-responsive T-cells that emerge after treatment with anti-CD4 monoclonal antibody (Mab). PPD-stimulated T-cell proliferations, OX40 phenotype and protein tyrosine phosphorylations involving p56^lck (pp56^lck) were compared to Con A stimulations using T-cells isolated from spleen and draining lymph node of CFA/PPD-immunized rats either untreated or treated in vivo with anti-CD4 Mab. Splenocytes stimulated by concanavalin A (Con A) showed correlated increases in proliferation, levels of pp56^lck, and OX40 expression; these parameters were not correlated in splenocytes after PPD-stimulations. T-cells isolated from lymph nodes draining the site of CFA/PPD immunization proliferated in response to stimulation by either PPD or Con A, but only PPD-responsive cells showed correlation to the OX40 activation phenotype and increased levels of pp56^lck. CD4⁺ T-cells isolated from either tissue compartment after anti-CD4 Mab treatments showed higher background and PPD-stimulated proliferations, and expressed lower levels of OX40. In contrast, anti-CD4 Mab treatments reduced (60%) and abolished Con A-stimulated proliferations of splenocytes and lymph node T-cells, respectively. The effects of anti-CD4 Mab treatment on pp56^lck levels correlated only to the changes observed for Con A stimulations of splenocytes. These results demonstrate that PPD antigen-specific T-cell populations recovered from different tissue compartments were resistant to in vivo anti-CD4 Mab treatments and did not show the activation changes characteristic of CD4⁺T-cells after Con A stimulation.