Sensitized CD8 + T Cells Fail To Control Organism Burden but Accelerate the Onset of Lung Injury during Pneumocystis carinii Pneumonia

Abstract

ABSTRACT While CD8 + cells have been shown to contribute to lung injury during Pneumocystis carinii pneumonia (PCP), there are conflicting reports concerning the ability of CD8 + cells to kill P. carinii. To address these two issues, we studied the effect of the presence of CD8 + cells in two mouse models of PCP. In the reconstituted SCID mouse model, depletion of CD8 + cells in addition to CD4 + cells after reconstitution did not result in increased numbers of P. carinii cysts compared to the numbers of cysts in mice with only CD4 + cells depleted. This result was observed regardless of whether the mice were reconstituted with naïve or P. carinii -sensitized lymphocytes. In contrast, reconstitution with sensitized lymphocytes resulted in more rapid onset of lung injury that was dependent on the presence of CD8 + cells. The course of organism replication over a 6-week period was also examined in the CD4 + -T-cell-depleted and CD4 + - and CD8 + -T-cell-depleted mouse model of PCP. Again, the organism burdens were identical at all times regardless of whether CD8 + cells were present. Thus, in the absence of CD4 + T cells, CD8 + T cells are a key contributor to the inflammatory lung injury associated with PCP. However, we were unable to demonstrate an in vivo effect of these cells on the course of P. carinii infection.