This type of reaction occurs when specific types of white blood cells (called T helper cells) respond to antigens and release toxic and inflammatory substances that can damage tissues. Cell-mediated immune reactions can occur in any organ. Treatment usually involves the use of anti-inflammatory drugs and drugs that suppress the immune system, either alone or in combination.
Granulomatous reactions are masses of fibrous connective tissue infiltrated by the white blood cells that form a cell-mediated immune response. The feline infectious peritonitis virus and some bacteria and fungi may trigger these reactions in cats. These reactions may be due to long-lasting cell-mediated immune reactions. Although cell-mediated immune responses effectively fight off these infections in most cats, in a few animals the immune response is only partially effective and results in the mass at the site of infection.
Last full review/revision July 2011 by Christine Andreoni; Kevin T. Schultz, DVM, PhD