Microsporidia (phylum Microsporidia) are intracellular parasites that infect a wide range of protozoa, invertebrates and vertebrate hosts. Over a 1000 species have been classified finto approximately 100 genera. Historically, microsporidial infections in silkworms, honey bees, and sahnonid fish have been responsible for significant economic losses. More recently, microsporidiosis has been recognized as an important opportunistic infection in immunologicaly compromised patients. In this review there is information on the immunobiology of microsporidia Encephalitozoon cuniculi and Encephalitozoon intestinalis which esere identified as the most common causative agents of microsporidiosis in mammals. Most of what is known about the immunology of microsporidiosis is based on experiments with the microsporidian Encephalitozoon cuniculi.

        Key words: Encephalitozoon cuniculi - Encephalitozoon intestinalis - microsporidia - opportunistic immunodeficiency.