To facilitate a detailed investigation of pinniped lymphoid organs, 30 monoclonal antibodies (mAb) as well as eight polyclonal antibodies (pAb) of different species specificities directed against cell antigens of the hematopoietic system were tested for immunohistochemical cross-reactivity on formalin-fixed, paraffin wax-embedded tissues of harbor seals (Phoca vitulina) and a walrus (Odobenus rosmarus rosmarus). Six monoclonal and eight polyclonal antibodies showed specific immunoreactivities. Lymphocytes were immunolabeled by an anti-CD3 pAb, anti-Foxp3 mAb and anti-CD79 alpha mAb, while plasma cell subpopulations were recognized by anti-IgA pAb, anti-IgG pAb and anti-IgM pAb as well as by anti-kappa- and anti-lambda light chain pAb. Cells of the histiocytic lineage were recognized by lysozyme-, myeloid/histiocyte antigen-, and CD68-specific markers. Furthermore, dendritic cell-like cells were detected by an anti-S100 protein pAb. The MHC class II antigen was labeled on the majority of immune cells of the harbor seal and walrus using a bovine mAb. Mast cells were stained by an anti-mast cell tryptase mAb. Thus, using these antibodies from various species, it is now possible to determine phenotypical changes in lymphoid organs and detect different leukocyte subsets involved in inflammatory responses in archived tissue samples of these pinniped species.
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