Concentrations of Pneumococcal IgA and IgM are compromised in some individuals with antibody deficiencies.

The response to pneumococcal vaccination is assessed by measurement of antigen specific IgG only and is compromised in a number of antibody deficiencies. We measured the concentrations of Pneumococcal IgA and IgM in individuals with both normal and abnormal pneumococcal capsular polysaccharide (PCP) IgG concentrations. A higher number of individuals had abnormal pre-vaccination IgA and IgM concentrations below the lower limit of the normal range compared to the control group. Post vaccination a lower number of individuals had IgA and IgM concentrations below the upper limit of the normal range compared to the control group. Non responders had a higher percentage of individuals with a prior history of infection. In addition, individuals with a history of prior infection had lower pre- and post-vaccination concentrations of PCP IgG, IgA, and IgM. Post-vaccination IgA and IgM concentrations identified four groups of responses which correlated with prior history of infection. A higher percentage of individuals with abnormal PCP IgA and IgM concentrations had a history of prior infection compared to the percentage of individuals with normal concentrations. In individuals with an antibody deficiency, measurement of Pneumococcal IgA and IgM correlates with the number of individuals with prior history of infection.

Measurement of the IgG2 response to Pneumococcal capsular polysaccharides may identify an antibody deficiency in individuals referred for immunological investigation.

IgG2 is the most efficient subclass for providing protection against pneumococcal pathogens. We hypothesised that some individuals may be unable to mount an effective pneumococcal capsular polysaccharide (PCP) IgG2 response despite having a normal PCP IgG concentration (PCP IgG2 deficient). The median pre-vaccination PCP IgG2 concentration was significantly lower in individuals referred for immunological investigation compared to healthy controls (2.8 mg/L range, 95% CI 1.1-88 vs. 29.5mg/L, 95% CI 13.5-90, p = 0.0002). PCP IgG:IgG2 ratios were significantly higher for the referral population than for healthy controls suggesting the increased production of PCP specific subclasses other than IgG2. The percentage of individuals with PCP IgG2 deficiency was significantly higher in referral groups compared to controls (31% vs. 5%; p = 0.0009) and in an individual with PCP IgG2 deficiency, the balance of PCP specific IgG subclass antibodies post vaccination changed from IgG2>IgG1>IgG3>IgG4 to IgG1>IgG3>IgG2>IgG4. The median PCP IgG2 concentration in those with PCP IgG2 deficiency was significantly lower in the referral groups compared to controls (7.8 mg/L, 95% CI 1.1-12 vs. 12.7 mg/L, 95% CI 11.8-13.1; p = 0.006). The data suggests a defect in the production PCP IgG2 may be present in individuals with normal PCP IgG referred for immunological investigation.