Primary immunodeficiencies of horses

Primary immunodeficiency disorders are genetically determined failures of i mmune defense that increase susceptibility to infectious agents. This artic le reviews the salient features of equine primary immunodeficiency disorder s, summarizes the molecular mechanisms of each disorder, and updates inform ation that facilitates diagnosis and management of affected horses. The cen tral theme is to encourage clinicians to ask, "I wonder if this horse has a n underlying primary immunodeficiency disorder?" when caring for horses suf fering from chronic and recurring infections and responding poorly to stand ard therapy.