Acquired immunity and reticuloendothelial system, Slides of Physiology

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Mechanisms of tolerance

• During the development of T cells in thymus
• T cells with TCR that recognize self proteins are eliminated and that do not recognize are retained Mechanisms-
• Clonal deletion
• Clonal anergy
• Suppression

Development of B cell

Stem cell of B cell in Bursa equivalents

Pre B cell

Naive B cell

Migrate to secondary lymphoid organs after maturation

Antigenic stimulation

Specific B cell clone

Plasma cell from B cell

Specific antibody from plasma cell

Plasma cell

Plasma cell (Short note)

• Seen in medullary cord of lymph node
• Originate from activated B cell
• Life span is 2-3 days
• Structure- oval, eccentric nucleus (cart wheel), basophilic cytoplasm, abundant ER, polyribosome and GA
• Secrete antibody

Cell Mediated Immunity

• Mediated by T cell

Mainly against

1. Viral infections
2. Fungal infections
3. Tumour cells
4. Transplanted cells
5. Chronic bacterial infections like TB, brucellosis
6. Parasitic infections

TYPES OF CELLULAR IMMUNE

• Primary cellular response RESPONSE

which is produced by an initial contact with a foreign antigen

• Secondary cellular response
• which is produced when the host is subsequently exposed to the same antigen.it is usually more pronounced and occurs more rapidly.

1. Antigen recognition, processing

and presentation

• T cells are activated only when the antigen is processed and presented by antigen presenting cell
• Intracellular pathogens are presented by nucleated cells
• APCs include macrophages, dendritic cells and B cells (extracellular pathogens)

• Antigen entering the host body is phagocytosed and degraded into polypeptide fragments by the antigen presenting cells (APCs).
• The antigen polypeptide fragments then become associated with the MHC antigen and are expressed on the surface of APC.

Recognition of antigen by

lymphocytes

• T lymphocytes possess the antigenic recognition receptors known as T cell receptors.
• These receptors serve as a specific surface receptors recognizing and interacting with only single antigenic determinant on the antigen presented to lymphocytes.

2.T lymphocyte différentiation

(activation)

The CD 8 + type of T lymphocytes after combining with foreign antigen–MHC-I complex are activated and differentiated into:

• Cytotoxic T cells (TC cells) and
• Suppressor T cells (TS cells).
• CD 4 + type of T lymphocytes after combining with foreign antigen–MHC-II complex are activated and differentiate into:
• Helper T cells (TH cells) and
• Delayed-type hypersensitivity T cells (TD cells).

• T lymphocyte memory cells are also formed. These spread throughout the lymphoid tissues of entire body.
• Therefore, on subsequent exposure to the same antigen, release of T cells occurs far more rapidly and much more powerfully than in first response (secondary response)