Anti-CD11b monoclonal antibody in an infant rat model of Haemophilus influenzae type b sepsis and meningitis.

Five-day-old infant rats were injected intraperitoneally (i.p.) with anti-CD11b monoclonal antibody (1 B6) at a dose of 2 mg/kg or phosphate-buffered saline (PBS) either 1 h before or 3 or 24 h after inoculation with 10(5) cfu Haemophilus influenzae type b (Hib). When administered 1 h before infection, 23% of the 1B6- versus 17% of the PBS-treated rats and 87% of the 1B6- versus 83% of the PBS-treated animals died at 24 and 48 h, respectively. There was a similar mortality for 1B6 or PBS treatment at 3 h after infection. Thirteen of 15 (87%) 1B6 animals versus 16/17 (94%) PBS animals had positive CSF cultures at 48 h. No differences in mortality were observed in separate experiments where animals received 1B6 or PBS 3 or 24 h after infection with Hib and were treated with a single ampicillin dose (100 mg/kg) 24 h after infection. The median CSF white blood cell count/mm3 was 5627 and 4860 for the animals with meningitis receiving 1B6 and PBS, respectively, although the 1B6-treated animals had a lower percentage of polymorphonuclear cells in the CSF (P = 0.05). Histologic examination of the meninges, choroid plexus and cochlea showed a slight decrease in the numbers of inflammatory cells in animals treated with 1B6. 1B6 did not change the incidence of meningitis and only slightly decreased the degree of inflammation within the central nervous system, although animals treated with 1B6 have an altered CSF leucocyte response with the presence of more mononuclear cells as opposed to polymorphonuclear cells in their CSF. 1B6 may play a role in inhibiting neutrophil emigration to sites of inflammation within the central nervous system but is not beneficial in decreasing mortality in an infant rat model of H. influenzae type b sepsis and meningitis.