Immunoglobulin subclasses and specific antihemophilus influentiae response in children with recurrent infections

Recurrent infections are known to occur in patients with an impaired humoral immune response. To evaluate the relative importance of immunoglobulin subclasses and specific antibody determinations we studied 70 patients referred to our immunology clinic because of recurrent infections and with normal concentrations of IgGs. Mean and median ages were 3.8 and 2 years, respectively. Each of the patients had determination of serum concentrations of IgA, IgM by nephelometry, and IgG subclasses by radial immunodiffusion. Serum immunoglobulin and IgG subclasses were considered “low” if they were more than 2 SD below the normal age-appropriate geometric mean. Considering the high incidence of Hemophilus in- fluenzae type b (Hib) disease in the 0–5 years age group natural specific antihemophilus influenzae response was also evaluated in a subpopulation of 40 children. Thirty-seven out of 70 patients (53%) showed immunologic abnormalities. Twenty-one out of 70 patients (30%) had subclass deficiencies, of which 13 had normal immunoglobulin isotype concentratoins. IgG2 was an isolated defect in 8 patients, IgG3 in 4 patients, and a combined subclass defect was found in only 1 patient. One third of the study population had associated atopy and 12 of these patients showed mild serologic immune abnormalities. All but 3 patients showed normal/high natural anti-Hib antibody concentrations; a subclass defect was found in all hyporesponsive children. Our findings show that a high proportion of children with recurrent infections have a demonstrable immunologic abnormality; however, the identification of these patients is not indicative of an inability to form antibodies to specific infectious antigens.