what is antigenic activity?

Antigenic activity is the ability of a chemical compound (usually a
protein or peptide) to elicit an immune response in a host. The large
number of clonal variants in the host and the ability of those clones to
mutate allow the host to respond to virutally an unlimited number of
antigens. The antigens are taken up by the host by a number of different
means and are processed by the immune system. Usually this involves
phagocytosis and partial digestion by macrophages. The processed antigen
is then presented to immune compartment cells (T cells and B cells), which
clonally expand in response to activation. The presentation of antigen can
occur in the gut or other mucosal lymphoid compartments. The activated
immune cells are often expanded in regional lymph nodes.