Distribution of IgM- and IgG-containing cells during the primary immune response in the rat spleen.

The morphology and localisation of IgM- and IgG-containing cells in the spleen of rats immunized with sheep red-blood cells (SRBC) were studied by combining immunohistochemical reactions with routine histological and histochemical methods. It was shown that IgM cells occur only in the outer periarteriolar lymphocyte sheath (PALS), whereas IgG cells are present throughout the whole PALS. It has been concluded that these cell types have different routes of migration. Both IgM- and IgG-containing cells were found in the germinal center in close relation with the extracellular immune complexes. The significance of this localisation is discussed.