Cellular immunity to the P6 outer membrane protein of nontypeable Haemophilus influenzae

Cellular immunity to nontypeable Haemophilus influenzae in a population of 10 healthy, immune adults was determined by measuring lymphocyte blast transformation and antibody secretion in response to the P6 outer membrane protein. P6 (200 μl/ml) induced lymphocyte blast transformation that peaked on day 10 of incubation. The peak induction of antibody-secreting cells occurred on day 8 of incubation. In comparison with the response to tetanus toxoid stimulation, the peak lymphocyte blast transformation response to P6 was reduced (mean counts per minute ± standard error of the mean [SEM], 3,457 ± 503 versus 9,414 ± 1,464; P = 0.0051) and delayed (mean days ± SEM, 10.3 ± 0.4 versus 8.4 ± 0.5; P = 0.0169); however, P6 was a better stimulus of antibody secretion from lymphocytes, particularly antibody of the immunoglobulin M (IgM) class (mean peak numbers of antibody-secreting cells per 10⁵ peripheral blood mononuclear cells ± SEM: IgG, 85 ± 29 versus 42 ± 16 [P = 0.0469]; IgM, 81 ± 20 versus 25 ± 7 [P = 0.0125]; IgA, 24 ± 8 versus 16 ± 6 [P = 0.0526]). Thus, lymphocytes from immune individuals recognize P6 of nontypeable H. influenzae as an immunogen. These data provide a basis for future studies with otitis-prone children who fail to develop a normal antibody response to P6 antigen (N. Yamanaka and H. Faden, J. Pediatr. 122:212-218, 1993).