New Rat Model ofPneumocystisPneumonia Induced by Anti-CD4+T-Lymphocyte Antibodies

The CD4+T lymphocyte plays a central role in host defense againstPneumocystispneumonia but has received only limited attention in rats. CD4+T-cell-depleting (OX-38) and nondepleting (W3/25) monoclonal antibodies, which recognize an identical or adjacent epitope, were administered for up to 14 weeks to Lewis rats that had been exposed toPneumocystis. While OX-38 produced a greater decrease in circulating CD4+cells than W3/25, both antibody treatments resulted in similar effects on the health of the rats and the levels ofPneumocystispneumonia, which were milder than those found with corticosteroids. W3/25 also did not enhance the severity ofPneumocystispneumonia achieved with corticosteroids alone. We conclude that CD4+cell function is more important than CD4+cell number in host defense againstPneumocystisin the rat and that this new model permits study of opportunistic infections in the rat without the confounding effects of corticosteroids.