Once an individual is infected with a human astrovirus, the astrovirus particles replicate within the intestinal tissue, specifically the epithelial cells in the lower regions of the villus.  The astrovirus virion is regarded as a foreign particle by the host's immune system, and a cell-mediated response occurs.  If a person becomes infected with one serotype but has previously been infected with another serotype, the person will develop both IgM  and IgG responses to the serotype to which he had been first exposed.  This anamnestic response shows antigenic relatedness between all serotypes of astrovirus.