Adjuvant

Adjuvant is derived from Latin word ‘adjuvare’ meaning to help. Adjuvant are materials that when with antigen increases the immunity of an organism. It helps in primary and secondary response improvement when small amount of antigen is present. For instance BSA (Bovine Serum Albumin) administered mice may develop five fold increased antibody response. How adjuvant augment increase the immune response is not precisely understood so far.

Effects of adjuvants

• It enhances the co-stimulatory signals
• Increases local inflammation
• Antibody is retained for longer time period
• It stimulates lymphocytes proliferation in a non specific way.

Instance for adjuvant

Alum:

Aluminum potassium sulfate, a salt increases the existence of specific antigen. Alum is mixed with antigen. Salt starts precipitating when it reacts with antigen. Alum precipitate is injected. Antigen is slowly released inside the injected site. Exposure of antigen without adjuvant slowly increases from few days to several weeks when antigen with adjuvant is exposed after a very few weeks of injection. It also helps in antigen size increasing thereby phagocytosis occurs.

Water oil:

This water oil adjuvant is referred as Freund’s incomplete adjuvant. Here antigen is mixed with aqueous solutions like mineral oil with the help of emulsifying agent. Mannide monooleate acts as emulsifying agent. Oil gets dispersed slowly in to injection site when it surrounds antigen. Freund’s complete adjuvant includes a microbial agent in addition to incomplete adjuvant. Heat killed mycobacteria acts as microbial agent. Cell wall of mycobacteria is Muramyl dipeptide. It activates macrophages. Activated macrophages can act as phagocytes. They increase the expression of cells like class II MHC molecules to T helper cell and B7 molecules to CD28. Adjuvants increase the co stimulatory signals and antigen presentation.

Other adjuvants:

Synthetic polyribonucleotide and bacterial LPS (Lipopolysaccharides) increase the nonspecific T lymphocyte proliferation of cells. This leads to clonal selection of lymphocytes by inducing antigen.