Abstract
Groups of 12โweekโold Balb/c mice were inoculated intranasally with respiratory syncytial virus (RSV) and sacrificed at regular intervals after infection. T lymphocyte subset distribution was determined in lung tissue, bronchoalveolar lavage (BAL), peripheral blood, and spleen by means of flow cytometry employing monoclonal antibodies against the T cell membrane antigens Thyl.2 (panโT), Ly2 (CD8), and L3T4 (CD4). Thyl.2^โฒ^ cells increased in the lung from 35.4% of total lymphocytes before infection to 47.6% on day 7 after infection. This increase was largely accounted for by an increase in Ly2^+^ cells, which manifested a rise from 7.8% preinfection to 19.8% on day 7. The level of L3T4+ cells remained constant (27.9% preinfection vs. 25.2% on day 7). The L3T4^+^/Ly2^+^ ratio in the lungs reached a nadir 7 days post infection (1.5 vs. 3.5 before infection). The total cell count in BAL increased more than tenfold during the first week after infection. At the same time Thyl.2^+^ cells in the BAL increased from 41.1% of total lymphocytes on day 1 to 85.3% on day 7. Ly2^+^ influx was the most important (5.8% on day 1 vs. 41.1% on day 7). L3T4^+^ cell levels increased from 17.2% on day 1 to 40.1% on day 7. RSVโspecific lymphocyte transformation was observed in BAL and blood but not in the lung tissue and spleen on day 7 postinfection. The disappearance of infectious virus in the lung correlated directly to the peak appearance of Ly2^+^ T cells in the lung tissue and BAL.