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In search for a possible explanation of the phenotypic heterogeneity in selective immunoglobulin (Ig)A deficiency, we studied the IgG2 antibody response to meningococcal polysaccharide A (PSA) in IgA-deficient (IgAd) individuals after vaccination with meningococcal A + C polysaccharide vaccine. Two groups of IgAd individuals, one frequently infected and one clinically apparently healthy, as well as healthy controls, were studied. In response to meningococcal A + C polysaccharide vaccine, a significant titre increase of specific IgG2 anti-PSA was found in 71% of the control individuals, in 50% of the healthy and in 42% of the infection-prone IgAd individuals. The specific IgG2 response against meningococcal PSA was significantly lower in the infection-prone IgAd individuals compared to the controls (P < 0.05). Among the IgAd individuals who responded with a significant IgG2 antibody increase, the IgG2 antibody response was significantly lower in the infection-prone than in the healthy IgAd individuals (P < 0.05). Thus, a limited capacity to mount a specific IgG2 response may suggest a more profound antibody maturation defect in infection-prone IgAd patients compared to healthy IgAd individuals.

Alterations in duodenal Ig-producing cells induced by two oral cholera vaccinations were studied by two-colour immunofluorescence in mucosal tissue sections from adults with selective IgA deficiency (IgAD), either with (n = 7) or without (n = 9) frequent infections, infection-prone patients with combined IgAD and IgG subclass deficiency (IgGSD) (n = 7), and normal control subjects (n = 11). The proportion of IgG-producing cells prior to immunization tended to be lower in the symptomatic IgAD subjects than in the clinically healthy ones. In the first subgroup the absolute number of IgG cells per intestinal length unit was significantly increased after immunization (P < 0.04), and this tendency was also observed in the healthy IgAD subjects (6/9) and in those with combined deficiency (5/7). Very few IgAD subjects responded with an increase of IgM-producing cells. The normal controls responded variably in all major immunocyte classes, in the order IgA > IgG > IgM. Compared with these controls, the patients with combined IgAD and IgGSD showed significantly increased IgG1 (P < 0.01) and reduced IgG2 (P < 0.006) proportions, which was in accordance with their serum subclass levels. Our study showed that oral cholera vaccination preferentially activates intestinal IgG-producing cells in IgAD subjects. This result agreed with data recently obtained by ELISPOT in the same patients with regard to antibody-forming cells specific for cholera toxin. Both methods suggested that IgG rather than IgM antibodies are elicited as compensation for a lacking IgA response. However, our overall results showed that intestinal B-cell activation is quite variable after oral cholera vaccination. Although such vaccination might be of importance for enhancing mucosal immunity also in IgAD patients, a concurrent gut disease could possibly be aggravated by IgG-mediated mucosal immunopathology in the absence of anti-inflammatory IgA antibodies.

The antibody levels and relative avidity of serum IgM and IgG antibodies against E. coli O antigens, poliovirus type 1 and beta-lactoglobulin were determined with enzyme-linked immunosorbent techniques in IgA deficient (IgAd) patients with frequent respiratory tract infections and healthy IgAd individuals. Healthy individuals with normal immunoglobulin levels served as controls. The IgM antibody levels against the bacterial, viral and food antigens and the IgG antibody levels against the bacterial antigens were significantly higher in the IgAd group with recurrent infections than in the group of healthy IgAd individuals. The symptomatic IgAd group had significantly higher levels of the IgG antibodies against the bacterial antigen, also when compared with controls. In contrast the healthy IgAd individuals had the highest avidities of IgM antibodies to the viral and food antigens. The high avidities of antibodies could be a compensatory host defence mechanism in IgAd. These aberrations may appear as a consequence of increased mucosal exposure in IgAd to antigens such as E. coli or beta-lactoglobulin, but presumably not to poliovirus which is only exceptionally present in the milieux. They could also be a result of the previously suggested dysregulation of antibody responses in IgAd.