Cells of the immune response

Table 1: Cells commonly found in the blood. Other cells that are seen include all types of immature progeinitor cells and endothelial and endomyocardial progenitors

Red blood cells
Platlets
White blood cells
	Granulocytes
		Polymorphonuclear cells
		Eosinophils
		Basophils
	Agranulocytes
		Lymphocytes
		Monocytes

The cells of the blood consist of red blood cells, white blood cells and platelets, see table 1. The white blood cells may be divided into polymorphonuclear cells, lymphocytes, monocytes, basophils and eosinophils. Unlike the red blood cells and the platelets the white blood cells frequently exit the circulation. The polymorphonuclear cells will go to a site of injury and try to kill anything that it does not like. Lymphocytes play a role in conducting the orchestra of the immune system. Monocytes will change into macrophages when suitably stimulated. The lymphocytes are broadly divided into B cells and T cells. The B cell produces antibodies and the T cells may be cytotoxic, helpers or suppressors.

Figure 4: Schematic representation of the afferent and efferent arms of the immune response. APC: antigen presneting cell, T$_h$: T helper cell (CD4+), T$_c$: Cytotoxic T cell (CD8+), B: B cell, M$_0$: Monocyte, NK: Natural Killer cell. The antigen is presented by the antigen presenting cell. Certain T$_h$ and T$_c$ cells will bind with the antigen presented with the antigen bound to self MHC protein on the surface of the antigen presenting cell. This stimulates the T cells to mount a response to the antigen via antibondy production, non-specific cytotoxicity and specific/direct cytotoxicity.

In essence the function of the immune system is to protect the self from non-self. It is necessary to have a system in place to fight off pathogens such as viri, bacteria and parasites. It would also be nice if this system could play a role in killing cancer cells. At the same time it is not a good idea for the immune system to damage the self.

The function of the immune system may be conceptualised into afferent and efferent arms, see figure 4. The afferent arm consists of;

Information gathering and presentation

which is done primarly by the antigen presenting cells

Computation and recruitment

which is done mainly by helper T cells both locally and remotely

The efferent arm of the immune response consists of;

Antibody mediated response

B lymphocytes produce antibody which binds with antigen, activates complement etc.

Non specific cell mediated response

is performed by macrophages and natural killer cells in response to stimulation by helper T cells

Specific cell mediated response

is mediated by specific cytotoxic T cells