Development of IgG responses to mycobacterial antigens.

Recent studies link mycobacterial and human heat shock protein antigens with autoimmune diseases. Little is known about the development of antibody responses to these antigens in children. IgG responses to mycobacterial antigens were studied in children living in the UK (an environment low in mycobacteria) who had not received BCG vaccination. Age curves of IgG response to sonicates from different species of mycobacteria were similar suggesting that the greater part of the developing IgG response is to the common antigens shared by all mycobacteria. The major part of the IgG response was to carbohydrate antigens: lipoarabinomannan is a mycobacterial cell wall carbohydrate and was confirmed as a major immunodominant antigen. Infants showed a marked early response to the mycobacterial 65 kilodalton (kDa) and 70 kDa heat shock proteins, but not to the human 65 kDa heat shock protein. The early IgG response to heat shock proteins may reflect cross reactivity to proteins released by a wide variety of bacteria (possibly from breakdown in the gut) or recognition of other immunodominant antigens with high levels of cross reactivity to self.