ABSTRACT
The extent and duration of antigenic stimulation is the major determinant of immunoglobulin levels in the blood and body fluids. Animals reared under germ-free conditions have low levels of immunoglobulins in the blood (hypogammaglobulinemia), whereas individuals with chronic infections have high levels (hypergammaglobulinemia). There are many chronic infectious diseases in which infection persists because of a failure of the immune response to eliminate the causative agent; examples are malaria, leishmaniasis, and hepatitis. There are other, mostly viral, infections in which the immune response fails to clear the infection because of the relative invisibility of the infectious agent to the immune system (as in herpes simplex and hepatitis C virus infection).
