Microbial Pathogenesis & Infectious Diseases

Immune Responses to Pathogens

Immune responses to pathogens: The function of the immune system is to protect humans from foreign agents and infectious organisms. The immune system consists of two functional mechanisms:

1.  Innate or non-specific immune system

2. Adaptive or specific immune system

​​​The innate immune system

The workings of the innate immune system provide a first line of defense against infection. Physical barriers to infection include skin, which prevents pathogen penetration, and bodily fluids like mucus, which collect and clear pathogens.

There are also a number of cellular and biochemical components, including complement proteins, innate leukocytes and phagocytic cells, which used to identify and eliminate pathogens from the body.

The adaptive immune system

The adaptive immune system is triggered when the innate system fails to clear pathogens from the body. It consists of a variety of cells and molecules, among which lymphocytes and antibodies are the key elements. Lymphocytes arise continuously from progenitor cells in the bone marrow. Lymphocytes synthesize cell surface receptors that specifically bind to foreign molecules. These secreted proteins are known as antibodies. The  molecule which bind to an antibody is called an antigen.  Pathogens bound to antibodies are marked for clearance or destruction. The functions of the adaptive immune system can be grouped into three basic types: B cells, Cytotoxic T cells (TC cells), Helper T cells (Th cells).