Immune system

An Immune system is a collection of biological processes within an organism that protects against disease by identifying and  killing pathogens and tumour cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own healthy cells and tissues in order to function properly
Antigen  is  substance that stimulates the production of an antibody when introduced into the organism. Antigens include toxins, bacteria, viruses, and other foreign substances
Antibodies: 
(also known as immunoglobulins, abbreviated Ig) are gamma globulin proteins that are found in blood or other  bodily fluids   and are used by the immune system to identify and neutralize foreign objects, such as bacteria and viruses.
The major components

of the immune system are:

•Immunocompetent cells

•Antibodies

•Complement system

•Bone marrow

•Thymus

•Spleen

•Lymph nodes

•Tonsils

Immunocompetent cells:

1.T-lymphocytes {T-helper,T-suppressor,T-cytotoxic

(killer cells),T-memory cells}

2.Natural killer cells(NK-cells)

3. B-lymphocytes

4.Plasma cells

5.Macrophages

6.Granulocytes of the blood(Neutrophilic, Eosinophilic,

Basophilic Leucocytes)

7.Monocytes

8.Mesenhymal reticular cells

9.Epithelial reticular cells

10.Antigen Presenting Cells (APC) {Dendritic cells,

Langerhans’ cells of the skin, Kupffer’s cells of the Liver, Dust cells of the Lung etc.)

BONE MARROW

The marrow of all bones begins as active hematopoietic tissue or red marrow(RBM). During growth, development, and aging, portions of the active red marrow are replaced by adipocytes to form :
•Bone marrow is a general term for the soft tissue occupying the medullary cavity of a long bone, the spaces amid the trabeculae of spongy bone, and the larger haversian canals.

•There are 2 main types: red & yellow.

•Red bone marrow = blood cell forming tissue = hematopoietic tissue

•Red bone marrow looks like blood but with a thicker consistency.

•It consists of a delicate mesh of reticular tissue saturated with immature red blood cells and scattered adipocytes.

Lymphoid Nodules (Follicles): These occur in all lymphatic aggregates except the thymus. Active (lymphocyte-producing) nodules each have a dark-staining periphery, or mantle zone, that contains tightly packed small lymphocytes, and a light-staining core, or germinal center, that contains numerous immunoblasts (lymphoblasts), ie, lymphocytes stimulated by antigens to enlarge and proliferate.The lighter staining reflects the increased cytoplasmic volume and decreased nuclear heterochromatin that accompany lymphocyte activation.

LYMPH NODES

These are the smallest but most numerous encapsulated lymphoid organs. Scattered in groups along lymphatic vessels , they act as in-line filters of the lymph, removing antigens and cellular debris and adding Igs.

SPLEEN

The largest of the lymphoid organs. Splenic pulp is composed of many erythrocytes, leukocytes, and macrophages, as well as a variety of blood vessels, all suspended within a meshwork of mesenchymal reticular cells and fibers.

 White pulp consists of the lymphoid tissue surrounding each of the many central arteries; it has 2 major components. The sleeves of lymphoid tissue immediately surrounding each central artery are called periarterial lymphatic sheaths (PALS). These contain mainly T lymphocytes and constitute the T-dependent regions of the spleen.

Surrounding each PALS, or appended to one side, is the second component, the peripheral white pulp (PWP). PWP contains mainly B lymphocytes and usually includes a typical secondary lymphoid nodule with a germinal center.