Long lasting IgG subclass and antibacterial polysaccharide antibody deficiency after allogeneic bone marrow transplantation.

Serum IgG subclasses were measured by a competitive indirect immunoassay with monoclonal antibodies in 31 leukemic patients before and after bone marrow transplantation. Antibodies to Hemophilus influenzae type b (Hib) capsular polysaccharide were determined in 28 cases. Abnormally low or borderline subclass (mostly IgG2 and IgG4) levels were found late after transplant in 23 infected and noninfected patients. These levels persisted for as long as 25 months, in association with low or borderline IgA levels in 78% of the cases. IgG2, IgG4, and IgA often showed a parallel evolution, whereas IgG1, IgG3, and IgM often varied together in the opposite way. Class but not subclass deficiencies were more frequent in patients with graft-v-host disease (GVHD). Subclass abnormalities predominated in infected patients, with mean levels correlating with the severity of infections; however, the abnormalities are not clearly predictive of infections in individual cases. Most patients with Hib pneumonia showed virtually no IgG antibody response to Hib, and one-half of the patients had a moderate IgM and IgA response. In the whole series, many sera collected greater than 1 year after graft contained very low or undetectable antibodies. Correlation between anti-Hib antibody and IgG2 levels was significant but weak because of discrepancies that were only partially explained by the subclass distribution of the antibodies.