Normal IgG and impaired IgM responses to polysaccharide vaccines in asplenic patients

Asplenic patients are at increased risk for life-threatening infections wit h polysaccharide-encapsulated organisms, and reports of responses to polysa ccharide vaccines have been conflicting. Thirty-six asplenic patients and 1 5 healthy controls were immunized with pneumococcal, Haemophilus influenzae type b (Hib), and meningococcal vaccines. Antibody concentrations to Hib a nd pneumococcal serotypes 14 and 18C were measured by ELISA, IgG antibody r esponses to all three antigens were similar in asplenic patients and contro ls at 28 days following immunization. In contrast, asplenic patients had si gnificantly lower IgM concentrations in response to Hib (P<.05) and to both pneumococcal serotypes 14 (P<.005) and 18C (P<.001), IgA anti-Hib antibody was also lower in the asplenic group, as was total anti-Hib antibody measu red by RTA. These results document that IgG responses to polysaccharide vac cines are normal in asplenic patients. The impaired IgM responses of these patients may explain conflicting reports from studies that measured only to tal antibody-binding concentrations.