The formation of immunoglobulins by human tissues in vitro. 3. Spleen, lymph nodes, bone marrow and thymus.

The site of immunoglobulin formation in human tissues was studied with three techniques: incubation of tissue fragments with radioactive amino acids followed by autoradiographic analysis of the synthesized immunoglobulins, immunofluorescent staining of tissue sections and cell suspensions, and morphological examination. These studies showed that the spleen, lymph nodes and bone marrow synthesize IgG, IgA and IgM. In agammaglobulinaemia, one bone marrow sample showed no immunoglobulin synthesis, the other sample synthesized a trace of IgG. Immunofluorescent staining has demonstrated that in the spleen and lymph nodes plasma cells and large and medium-sized lymphocytes were positive for IgG, IgA or IgM; small lymphocytes were only positive for IgM. In bone-marrow samples, however, only plasma cells were positive for immunoglobulins. It is discussed whether in the bone marrow the cells that synthesize immunoglobulins do not originate in this organ, but derive from other lymphopoietic organs. The normal thymus showed a different pattern because it synthesized only IgG and IgA. The plasma cells and medium-sized lymphocytes, which synthesize immunoglobulins, were localized predominantly in the interstitial connective tissue and ocasionally in the medulla, both near blood vessels. In all likelihood these cells did not originate in the thymus, but were trapped in this organ from the circulation. In autoimmune diseases, however, the thymus showed IgM-positive germinal centres and plasma cells and synthesized IgG, IgA and also IgM.