Question

Diagram and briefly describe cells of the immune system and their basic functions. Start with hematopoietic stem cells, and proceed through each class and type of the immune system cells.

Answer 1

All blood cells arise from a type of cell known as Hematopoietic Stem Cell. HSC's are self-renewing. Stem cells are the cells which can differentiate into other cell types. Hematopoietic stem cells are multipotent or pluripotent which can generate:

1. erythrocytes
2. lymphocytes
3. granulocytes
4. monocytes
5. mast cells
6. megakaryocytes

In hematopoiesis, a multipotent stem cell differentiates either by giving rise to common lymphoid progenitor cell or common myeloid progenitor cell.

Common Lymphoid progenitor cells gives rise to

1. Natural killer cells : Activated in responce to interferons or macrophage derived cytokines. They kill infected cells
2. T-cell progenitor (differentiate to form )

• TH cells : T helper cells are Class II MHC restricted. They secrete cytokines to activate B-cells
• TC cells : Cytotoxic T cells are Class I MHC restricted. They eliminate altered self cells

3. B-cell progenitor : B cells synthesize immunoglobin molecules

4. Dendritic cell : They have long menbrane extensions. They express class II MHC molecules and members of co-stimulatory B7 family. More potent Antigen Presenting Cells to TH cells.

Myeloid stem cells generate

1. Dendritic cells
2. Erythroid progenitor (erythrocytes) : transportation of oxygen
3. Megakaryocyte (gives rise to platelets) : Clumps formation to initiate blood clots
4. Basophil progenitor (Basophils) : Nonphagocytic cells and release pharmacologically active substances that play a role in allergic responses.
5. Eosinophil progenitor(Eosinophil) : They are motile. They play a role in defence against parasitic organisms.
6. Granulocyte monocyte progenitor which gives off

• Neutrophils : Active phagocytes. They release lytic enzymes and bactericidal substances.
• Monocytes : Remove dead or damaged cells, destroys cancer cells. They give rise to macrophages, which are called scavenger cells