Antigenic Variation

This article discusses antigenic variation; the different mechanisms used by viruses to escape the host immune system and the resulting problems with vaccine design and/or production. We have focused on antibody selection and only briefly discuss T-cell selection. Historically, virus variants were defined by serology; a total lack of cross-reactivity means a different virus type and lack of cross-reactivity of a particular protein defines a subtype. Current definitions of relationships may rely more on sequence than serology, depending on the virus under study. Many virus groups show considerable antigenic variation and we will summarize the characteristics of the variation for some of the variable groups. We go into more details of mechanisms with two examples of particularly variable surface antigens: human immunodeficiency virus and influenza viruses.