Adaptive Immunity

Definition

The specific reactivity induced in a host by an antigenic stimulus is known as adaptive immune response.

The immune response includes reactions against any living or nonliving. It may lead to consequences that are beneficial, indifferent or injurious to the host. It also includes the state of specific non-reactive (immunological tolerance) induced by certain types of antigenic stimuli.

?

Types of Immune Response.

The immune response to an antigen is of two types:

1. Humoral immune response or antibody mediated immunity (AMI).

2. Cell mediated immune response (CMI)

The two types of immune responses are usually developed together, though at times one or other may be predominant or exclusive. They usually act in conjunction but may sometimes act in opposition.

Humoral Immune Response (AMI)

It is mediated by antibodies produced by plasma cells that are transformed B lymphocytes. AMI is primarily directed against

1.???? Extracellular bacterial

2.???? Respiratory and intestinal viral infections.

3.???? Recurrence of viral infections.

4.???? Toxin-induced diseases

5.???? Infections in which virulence is related to polysaccharide capsules (e.g. Pneumococci, Meningococci, Hemophilus influenza).

6.???? AMI also leads to the development of immediate (Types I, II, III) hypersensitivity reactions and certain autoimmune diseases.

Cell Mediated Immune Response (CMI)

It is mediated directly by sensitized T lymphocytes and macrophages, without involving antibodies and B lymphocytes.

CMI serves the following immunological functions:

1.???? Immunity against obligate and facultative intracellular bacterial diseases, e.g. Tuberculosis, Leprosy, Brucellosis, Listeriosis etc.

2.???? Immunity against viral, fungal (e.g. histoplasmosis, coccidioidomycosis, blast mycosis) and parasitic (e.g. leishmaniasis, malaria, toxoplasmosis, trypanosomiasis etc.) diseases.

3.???? Immunity against tumor cells (cancer) and immunological surveillance

4.???? Transplantation immunity-participates in graft rejection and Graft-versus-Host (GVH) reaction.

5.???? Delayed (type IV) hypersensitivity. (DH)

6.???? Pathogenesis of certain autoimmune diseases e.g. thyroiditis, encephalomyelitis.

?