Intestinal, Salivary, and Tonsillar IgA and J‐Chain Production in a Patient with Severe Deficiency of Serum IgA

An 18-year-old man with tendency to respiratory infections had a serum IgA level of only 2% of normal whereas his salivary IgA amounted to 50% of the lower normal concentration range. Moreover, both the rectal and jejunal IgA-producing cell populations were of normal size. Nevertheless, a relative increase of salivary IgM and a distinctly raised number of IgM-producing cells in jejunal mucosa indicated an imbalance in his secretory immune system. This possibility was supported by the presence of an excess of J 3 chains in most of his intestinal IgA immunocytes, probably reflecting a reduced synthetic rate of IgA. The number of tonsillar IgA-producing cells was only slightly below the normal range; most of them lacked J chain, as normal, and could thus be a source of his serum IgA, which was mainly monomeric. A marked deficiency of IgA-producing cells in his bone marrow supported the notion that this tissue site normally is the major source of monomeric IgA. This study suggests that a generally defective IgA system may be topically activated owing to the persistent antigenic and mitogenic load on mucosa-associated lymphoid tissues. Our findings are not consistent with a general regulative compartmentalization of monomer- and dimer-producing IgA immunocyte populations.