Mucosal T cells recovered from mice after infection with respiratory syncytial virus display a memory/activation phenotype

Pgp-1 expression was studied as a marker of memory/activation on systemic and mucosal T cells of BALB/c and C57BL/6 mice after infection with respiratory syncytial virus (RSV), using two-color dual fluorescence flow cytometry employing anti-L3T4 (CD4), anti-Ly2 (CD8), and anti-Pgp-1 (CD44) monoclonal antibodies. Pgp-1 was expressed in relatively low densities on T cells of C57BL/6 mice, allowing differentiation of a dual population of Pgp-1(10) and Pgp-1hi T cells after antigenic stimulation in vivo. On the contrary, T cells of BALB/c mice were uniformly Pgp-1hi, making this mouse strain less suitable for studies with this marker. In blood and spleen consistently more CD8+ than CD4+ T cells were Pgp-1hi, while in BAL more CD4+ than CD8+ T cells were Pgp-1hi. After primary but not after secondary infection, CD4+ Pgp-1hi T cells increased significantly in the blood and spleen. After secondary infection both CD4+ Pgp-1hi and CD8+ Pgp-1hi T cells increased in the BAL. It is hypothesized that after primary infection systemic RSV-specific T cells acquire an activation/memory phenotype as characterized by an enhanced expression of Pgp-1, resulting in a faster and stronger influx of these cells in the lungs after secondary infection.