VII - Immunology of the Dog

Abstract

The thymus is believed to be the main site of T cell development in dogs, and it consists of two main lobes and is situated in the cranial mediastinum. The spleen is a boot-shaped organ in the abdominal cavity, and its exact location depends on the fullness of the stomach. The main immune function of the spleen is to respond to blood-borne pathogens. Immunoglobulin A (IgA) is the major immunoglobulin of most external secretions in dogs. The serum IgA and secretory IgA exist predominantly as dimers with a J chain. The serum IgA is largely derived from plasma cells in the intestinal lamina propria, although significant IgA secretion by spleen and bone marrow cells has been observed in vitro. IgA is the predominant immunoglobulin isotype produced by plasma cells in the intestinal lamina propria. The number of IgA-secreting plasma cells decreases from the duodenum to the ileum. The transport of IgA across the epithelium into the lumen occurs via the polymeric immunoglobulin (poly-Ig) receptor that is expressed on the basolateral surface of the epithelial cells. The mucosal immune system encompasses the immune system of the gastrointestinal tract, the respiratory tract, the genital tract, the conjunctiva, and the mammary glands. The mucosal immune system can be divided into inductive sites and effector sites. The inductive sites include Peyer's patches (PPs) in the small intestine, the solitary lymphoid nodules in the stomach, the small and large intestine, the tonsils, the lymphoid nodules in the third eyelid, and the lymph nodes draining the mucosal tissues.