Expression of the alpha-chain gene in heterogeneous IgA immunodeficiency

Five heterogeneous IgA-immunodeficient patients were analysed for expression of the alpha-chain gene. The number of surface IgA-bearing B cells was low in four patients. Southern blot analysis indicated no deletion of immunoglobulin structural genes coding for C alpha or alpha switching-region genes. The number of surface IgM and IgA double-bearing B cells increased in some patients. Addition of recombinant interleukin 4 (rIL-4), rIL-5, and rIL-6 to the normal B cells enhanced IgA production. However, B cells of the patients showed no or one-third lower IgA production in response to these lymphokines, even though there was proliferation. rIL-4, rIL-5, and rIL-6 induced low or no expression of alpha mRNA of the patients' B cells. These results suggested that the patients lacked B cells able to produce transcripts for the IgA heavy chain, and that some patients' B cells might be defective at the switch-recombination process from mu to alpha or from mu and alpha to alpha.