What is Immunogenicity?

Immunogenicity of any antigen depends upon the biological environment in which it has to generate immune response. The immune response to antigen depends on the following factors of the biological system.

(1) Genetic constitution of the recipient:

Genetic constitution of the recipient influences the type and intensity of immune response to the antigen.

The receptors of T and B cells are under the control of genes. They play a key role in binding with antigens; hence their structural and molecular characteristics (controlled by genes) directly influence the antigen binding. Antigen binding is essential for initiation of immune response.

For example people with normal hemoglobin are susceptible to death from malaria, but people with sickle cell trait have a greater chance of surviving malaria and do not suffer adverse consequences, due to the presence of one gene for hemoglobin A and one gene for hemoglobin S. Sickle trait provides a survival advantage over people with normal hemoglobin in regions where malaria is endemic.

Hemoglobin C is also believed to protect against malaria Hemoglobin C heterozygotes had significantly fewer episodes of P. falciparum malaria than did controls with only hemoglobin A. The risk of malaria was lower still in subjects who were homozygous for hemoglobin C.

(2) Dose of antigens:

An insufficient dose of even an effective immunogen may fail to induce immune response in the host. To produce the immune response the immune system has to identify and recognize the antigen. If the dose of antigen is too low, the chances of encounter of this immunogen with T and B lymphocytes are remote.

Non specific phagocytes may remove these antigens from biological system, even before they interact with T and B cells. An excessive dose of antigens also fail to induce a response, because it causes lymphocytes to enter in to a no responsive state.

In case of certain antigens a single dose may not be sufficient to induce a strong response. Repeated administrations (booster doses) over a period of time may be required to stimulate strong response.

(3) Route of administration:

The encountering lymphocytes in different routes are different and the type of response depends on the type of lymphocytes encountering the antigen.

Hence the route of administration influences the immune response. For example cell mediated response can be expected for antigens introduced intra dermaly. If antigens enter the body through respiratory or gastric intestinal tract, IglA antibody mediated response can be expected. Because the B cell in those areas are committed to produce IglA antibodies.

Routes commonly used for immunization depend on the type of antigen. It may be intra muscular subcutaneous, intravenous, intraperitoneal, and intro dermal. In spite of the route of administration most antigens eventually become distributed through out the body by circulation and induce both humoral and cell mediated response.