ROLE OF T-LYMPHOCYTE SUBSETS IN RECOVERY FROM RESPIRATORY SYNCYTIAL VIRUS-INFECTION IN CALVES

The role of T-cell subsets in respiratory syncytial virus (RSV) infect ion was investigated by using monoclonal antibodies (MAbs) to selectiv ely deplete gnotobiotic calves of CD4(+), CD8(+), or WC1(+) gamma delt a T-cell receptor(+) lymphocytes. Injection of these MAbs produced spe cific reductions of the target cell populations in the circulation and tissues. Ten days after RSV infection, immunoglobulin M (IgM), IgG1, and IgA antibodies were detected in sera and lung washings from contro l calves. Depletion of CD8(+) T cells had no effect on either the seru m or local antibody responses to RSV, whereas depletion of CD4(+) T ce lls suppressed the antibody responses in two of three calves. The IgM and IgA responses were significantly increased in the lung washings of calves from which WC1(+) T cells were depleted. Depletion of CD4(+) o r WC1(+) T cells caused no significant delay in virus clearance, altho ugh an increase in the extent of pneumonic consolidation was observed in anti-CD4-treated calves, Nasopharyngeal excretion of RSV was prolon ged in calves depleted of CD8(+) T cells, and virus was isolated in hi gh titers from lung washings of these animals 10 days after infection, whereas virus had been cleared from lung washings of all other animal s. The delayed virus clearance was associated with an increase in the severity of pneumonic consolidation in three of four of the calves fro m which CD8(+) T cells were depleted. This study shows that CD8(+) T c ells play a dominant role in the recovery of calves from RSV infection .