Low IgG4 concentrations in infants with Haemophilus influenzae type b infections.

Haemophilus influenzae type b causes considerable morbidity and mortality in infants and young children. Immunity to this organism has been attributed in part to the formation, and increase with age, of antibodies to the capsular polysaccharide of the bacteria. A degree of immunodeficiency could explain why some infants and young children develop invasive haemophilus disease. In this study we investigated immunocompetence in ten infants with invasive haemophilus disease. We found normal lymphocyte mitogen responses, neutrophil iodination and bactericidal and fungicidal capacities in this group. While we found no deficiencies of any of the immunoglobulin classes, three patients had low concentrations of IgG4 and two of them had low concentrations of IgG2 as well. These findings suggest that in some infants who develop haemophilus infections, the measurement of IgG subclasses may reveal immune defects that would not otherwise be apparent.