An antigen, by definition, is a substance which binds to an antibody
molecule. Immunogens are antigens that elicit immune response, therefore
all immunogens are antigens but not all antigens are immunogens.
In other words, only those antigens that cause clonal selection and
expansion of T or B lymphocytes can be regarded as "immunogens". There
are some autoantigens that do not generate any response in the host and
there are some other antigens such as DNA that can barely generate any
immune response even across species.
However, if antigens meet certain criteria (e.g. high molecular weight,
complexity, flexibility, etc.) they become good immunogens.
Shayan Sharif
Department of Pathobiology
University of Guelph
Guelph, Ontario
Canada
