Lymphatic organs of normo- and dysgammaglobulinemic chickens were studied by immunohistochemical methods concerning IgM-, IgG-, and IgA-positive cells. IgM- and IgA-positive lymphocytes and plasmacytic cells are similarly distributed in dys- and normogammaglobulinemic chickens. Follicles of the bursa of Fabricius contain cortical lymphocytes weakly and medullar lymphocytes distinctly stained by anti-IgM, as well as some larger irregularly shaped cells with intensely labeled cytoplasm. In spleen, periellipsoid lymphocytes, some red pulp lymphocytes, and varying numbers of plasmacytic cells are also distinctly labeled by anti-IgM. IgA-positive lymphocytes are not present in the bursa of Fabricius, but the bursal medulla is populated by some irregular, mostly longish cells with cytoplasmic IgA reaction. Spleen contains a few IgA-labeled lymphocytes and plasmacytic cells. The only difference between normo- and dysgammaglobulinemic chickens is found in IgG-positive cells, which are absent in permanently dysgammaglobulinemic chickens. The results from dysgammaglobulinemic chickens show that IgA can also be produced in untreated chickens lacking IgG synthesis and suggest that the theory of an IgM → IgG → IgA sequence is unlik
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