A study of immunoglobulin classes present on the membrane and in the cytoplasm of human tonsil plasma cells.

The problem of whether immunoglobulin (Ig)-containing plasma cells expressed membrane Ig has been investigated using cells from human tonsils. In tonsils, IgG-containing cells are predominant, but a certain number of IgM, IgA and IgD-containing cells are also present. By using a double staining immunofluorescent technique for the simultaneous detection of membrane and intracytoplasmic Ig, it has been possible to ascertain that the large majority of IgA, IgM and IgD-containing cells had membrane immunoglobulin (mIg) of a class coincident with that of intracytoplasmic Ig. In addition a noticeable proportion of IgM-containing cells expressed membrane IgD, thus indicating that a certain number of these cells bore both membrane IgM and IgD. About 60% of IgG-containing cells had membrane IgG, while the remaining cells did not express mIg. Furthermore the surface staining of these cells was generally fainter than that of the cells containing other Ig classes. Experiments on the surface light chain type expressed by the single Ig-containing cells (IgCC) as compared to that found in the cytoplasm have shown that in the large majority of IgCC the light chain type of mIg coincided with that of intracytoplasmic Ig. Discordant light chain types of membrane and cytoplasmic Ig were found on about 12% of IgCC only. These values can be taken as a measure of how many IgCC had passively acquired mIg.