Immune

© 2002, G. Holzer, all rights reserved.

Immune System

Content : - immune response - white blood cells - cellular and humoral immune response

Immune response

Our environment is full of pathogens (bacteria, viruses, pollutants, etc). Our immune system is neutralizes these invaders. The non-specific immune response includes barriers such as skin and mucus secretions e.g. in our lungs or nose. The mucus can trap invaders and they can be flushed out. Nonspecific cellular response includes the engulfing and lysis of invaders by phagocytes. The inflammation reaction is also a nonspecific response.The paracrine hormone histamine is released, making blood capillaries leaky. The blood with its white blood cells will penetrate infected tissue initiating the immune response.
The specific immune response includes the the production of antibodies, their attachment to the antigen region of invadors and the final destruction of the tagged invaders.

Cells of the immune system

The human immune system ( image ) is organized into a host of individual cells, which arise in the bone marrow and circulate in blood and lymph. In humans the white blood cells (called leukocytes) are the agents of the immune response. The cells of the human immune system include

White blood cells that act through Phagocytosis

Phagocytes : (mostly in liver, spleen and lymph nodes) destroy invaders through phagocytosis
Macrophages : circulate in the lymph system and blood, engulf envaders (e.g. viruses or bacteria) and digest them (image) Macrophages are the first defense during an infection. Their numbers increase rapidly.
Monocytes: develop into macrophages during an infection.
Neutrophils: are similar to macrophages, i.e. they engulf invaders, however they also secrete a chemical that kills additional invaders on contact.
Eosinophils: digest invaders which are tagged by antibodies.

Lymphocytes

B-cells: produce antibodies and form memory cells. They develop in the bone marrow
T-cells: there are two types of T-cells: Cytotoxic T-cells which recognize infected cell and destroy them and T-helper cells which assist B-cells to develop antibodies.

Antigen and Antibodies
Every animal cell has glycoproteins embedded in the outer surface of the plasma membrane. These glycoproteins are known as Major Histocompatibility Complex (MHC) proteins. Most cells of the body contain so called Class I MHC markers, Class II MHC markers are restricted to macrophages, B-cells and activated Helper T cells. The genes which code for these MHC proteins are highly polymorphic (many different alleles in a given population). No two individuals have the same MHC proteins. An individuals own MHC proteins are ignored by the individual's immune cells. However, invaders are recognized by the immune cells because they have different MHC proteins and are attacked directly by phagocytes or are tagged with antibodies to be lysed by eosinophils.

Antibodies , Antibodies

The specific immune response follows two pathways, the cellular response and the humoral immune . The pathways include antigen recognition, processing , Tc cell activation (cellular response) and B cell activation (humoral response)