Autoimmunity is due to an abnormal immune response in which the immune system fails to properly distinguish between self and non-self and attacks its own body. Our body produces antibodies (auto antibodies) and cytotoxic T cells that destroy are own tissues. If a diseasestate results, it is referred to as auto-immune disease. Thus, autoimmunity is a misdirected immune response. Autoimmunity is evidenced by the presence of auto antibodies and T cells that are reactive with host antigens. When the cells act as antigens in the same body, they are called autoantigens. Eg., Multiple sclerosis is a autoimmune disease.

A simpl blood tes is available that can determine wheth r the person has been, infected with HIV. The ELISA test (Enzyme Linked ImmunoSorbent Assay) detects the presence of HIV antibodies. It is a preliminary test: Western blot test is more reliable and a confirmatory test. It detects the viral core proteins.r lf both tests detect the presence ofl:he antibodies, the person is corfsidered to be HIV positive. The vaccines are classified as first, second and third generation vaccines.
(i) First generation vaccine is further subdivided into live attenuated vaccine, killed vaccine and toxoids.
(a) Live attenuated vaccines use the weakened (attenuated), aged, less virulent form of the virus. E.g. Measles, mumps and rubella (MMR) vaccine and the Varicella (chickenpox) vaccine.
(b) Killed (inactivated) vaccines are killed or inactivated by heat and other methods. E.g. Salk's polio vaccine.
(c) Toxoid vaccines contain a toxin or chemical secreted by the bacteria or virus. They make us immune to the harmful effects of the infection, instead of to the infection itself. E.g. DPT vaccine (Diphtheria, Pertussis and Tetanus).
(ii) Second generation vaccine contains the pure surface antigen of the pathogen. E.g. Hepatitis- B vaccine.
(iii) Third generation vaccine contains the purest and the highest potency vaccines which are synthetic in generation. The latest revolution in vaccine is DNA vaccine or recombinant vaccine.

A vaccine is a biological preparation that provides active acquired immunity to a particular disease and resembles a diseasecausing microorganism and is often made from weakened or atlenuated or killed forms of the microbes, their toxins, or one of its surface proteins. The vaccines are classified as first, second and third generation vaccines.

opsonisation or enhanced attachment is a type of antigen-antibody reaction. It is a process by which a pathogen is marked of ingestion and destruction by a phagocyte. Opsonisation involves the binding of an opsonin i.e. antibody, to a receptor on the pathogen's cell membrane. After opsonin binds to the membrane, phagocytes are attracted to the pathogen. So, opsonisation is a process in which pathogens are coated with a substance called an opsonin, marking the pathogen out for destruction by the immune system. This results in a much more efficient phagocytosis.

Monocytes, neutrophils, tissue macrophages and phagocytes.