CD8(+) T cells have an essential role in pulmonary clearance of nontypeable Haemophilus influenzae following mucosal immunization

A rodent respiratory experimental model has proved useful for investigating the immune mechanisms responsible for clearance of bacteria from the lungs . Immunohistochemical studies in immune and nonimmune rats have identified the cellular kinetics of response to bacterial pulmonary infection for CD8( +), CD4(+), and gamma delta (+) T cells; B cells; and the expression of maj or histocompatibility complex class II (MHC-II). During the course of bacte rial clearance, there was no apparent proliferation or extravasation of lym phocytes, nor was there increased expression of MHC-II: in nonimmune animal s despite an influx of polymorphonuclear leukocytes, whereas in immunized a nimals there was an early influx of CD8(+) and gamma delta (+) T cells, fol lowed by enhanced expression of the MHC-II marker, cellular infiltration by polymorphonuclear leukocytes, and finally an increased number of CD4(+) T cells. Depletion of CD8(+) T cells confirmed their vital contribution in th e preprimed immune response to pulmonary infection by significantly decreas ing the animals' ability to clear bacteria following challenge.