Cells And Organs Of Immunity

Organs and Cells Of Immunity Dr. Mejbah Uddin Ahmed

Cells and Organs of Immunity Primary lymphoid organs: Lymphocytes differentiate to from lymphoid progenitor cells, proliferate and mature into functional effector cells. T lymphocytes develop in the thymus and B-lymphocytes in the bone marrow (and fetal liver).

Cells and Organs of Immunity Secondary lymphoid organs: Where lymphocytes interact with each other and with antigens order to disseminate as effector cells and secreted molecule (antibody). Secondary lymphoid organs include: lymph vessels, lymph nodes, spleen, Mucosa associated lymphoid tissue e.g. tonsils and peyer’s patches (MALT), skin associated lymphoid tissue (SALT).

Cells and Organs of Immunity

Cells and Organs of Immunity Cells of immunity: T Lymphocytes, B lymhocytes, Natural killer (NK) cell, Macrophages, Basophils

Monocytes, Neutrophils, Eosinophils, Mast cell.

Cells and Organs of Immunity

Cells and Organs of Immunity

Cells and Organs of Immunity Origin and development of immuno competent cells: In intrauterine life blood cells originate in yolk sac then in the foetal liver and finally in the bone marrow. In adults, bone marrow produces hemopoietic stem cells. Stem cells differentiate into cells of erythroid, myeloid and lymphoid series.

Cells And Organs of Immunity Origin and development of immuno competent cells: The latter evolve into two main lymphocyte: T cell and B cells. T cell develops into immunocompetent T cell within the thymus. Prior to entering the thymus, stem cells lack antigen receptors and CD3, CD4 and CD8 protein.

Cells And Organs of Immunity Origin and development of immuno competent cells:

The stem cells which initially express neither CD4 nor CD8 (double negatives). First differentiate into both CD4 and CD8 (double positives) and then proceed to express either CD4 or CD8. A double positive cell will differentiate into a CD4 positive cell if it contact a cell bearing class II MHC protein but will differentiate into a CD8 positive cell if it contact a cell bearing class I MHC proteins.

Cells And Organs of Immunity Thymic education: Within the thymus, T cell trained up by two important processes called thymic education. CD4 and CD8 positive cells bearing antigen receptor for “self ” proteins are killed (clonal deletion) by a process called apoptosis. The removal of this self reactive cells, a process called negative selection, results in tolerance to our own proteins.

Cells And Organs of Immunity Thymic education: CD4 and CD8 positive cells bearing antigen receptor that do not recognize “self ” proteins are also killed. The removal of this self reactive cells, a process called positive selection.

Cells and Organs of Immunity T cells: stored & mature in thymus-migrate throughout the body. Killer (CD8) Cells: Perform lysis of infected cells. Cell mediated immune response. Helper (CD4) Cells: Enhance T killer or B cell activity. Suppressor T Cells: Reduce/suppress immune activity. May help prevent autoimmune disease.

Cells And Organs of Immunity B-Cells: •secrete highly specific Ab to bind foreign substance (antigen: Ag), form Ab-Ag complex. •responsible for humoral response. •perform antigen processing and presentation. •differentiate into plasma cells (Ab secretion).

Cells And Organs of Immunity Neutrophils-found throughout body, in blood -important component of innate immunity. - phagocytosis and bactericidal. Natural Killer Cells- cells innate immunity -destroy cancer cells -stimulated by interferons.

Cells And Organs of Immunity Macrophages-throughout body, blood, lymphatics -phagocytose non-specifically. -phagocytose specifically Ab-Ag CX -have degradative enzyme. -perform Ag processing and presentation. -secrete lymphokines / cytokines to stimulate T helper cells and immune activity.

Cells And Organs of Immunity Eosinophils: •Granules contain destructive enzymes, include: acid phosphatase, peroxidase and proteinase. They are capable of phagocytosis but poor. The substances they release defend primarily against pathogens that are too big to phagocytosis (parasitic worms). Secrete leukotrienes, prostaglandins, chemicals that causes vasodilation and increased capillary permeability.

Cells and Organs of Immunity Basophils:

Basophils release histamine, leukotrienes , and prostaglandins , chemicals that promotes inflammation by causing vasodilation , increasing capillary permeability, and increasing mucous production.

Cells and Organs of Immunity Monocytes: Monocytes differentiate into macrophages when they leave the blood and enter the tissue. Monocytes are important phagocytes. Macrophages and dendritic cells are very important in phagocytosis and serve as antigen-presenting cells in the adaptive immune responses. They produce a variety of cytokines that play numerous roles in body defense.

Cells and Organs of Immunity Dendritic Cells: Dendritic cells are derived from monocytes. They are located throughout the epithelium of the skin, the respiratory tract, and the gastrointestinal tract. The primary function is to capture and present protein antigens to naive T-lymphocytes. Dendritic cells produce cytokines, namely (TNFalpha), interleukin-1 (IL-1), interleukin-6 (IL-6), and interleukin-8 (IL-8).

Cells and Organs of Immunity Mast Cells: Found throughout the connective tissue of the skin and mucous membranes. They release histamine, leukotriens, prostaglandins, chemicals that cause vasodilation, increase capillary permeability, and mucous production.