Double labeling immunohistological study of African swine fever virus-infected spleen and lymph nodes.

To identify cells in situ in which African swine fever (ASF) virus is present, a double immunohistological labeling technique was used on sections of ASF-infected spleen and lymph nodes. Cells were identified by an indirect immunoalkaline phosphatase technique using monoclonal antibodies (MoAb) reactive against different leukocyte subsets. ASF virus, detected by a direct immunoperoxidase method using swine immunoglobulin G (IgG) anti-ASF virus antigens, was not present in T helper or in T cytotoxic/suppressor lymphocytes, whereas it was detected in tissue macrophages that reacted with different MoAb (74-22-15, C4, A7, and F2). A large number of cells strongly reactive with MoAb 74-12-4 (T helper lymphocytes) were found in the marginal zone in infected spleen. In infected lymph nodes, these intensely stained cells were found in small numbers. Cells reactive with MoAb 76-2-11 (T cytotoxic/suppressor lymphocytes) were less stained in infected spleen and lymph nodes than in non-infected organs.