How does the immune system respond to the invasion of a pathogen? What are the first few steps of response?

 

Innate is the first line of immunological response towards a pathogen because it is rapid, initiates within minutes and has no memory. Adaptive immunity is an antigen-dependent response which involves a long time between the pathogen exposure and immunological response.(Janeway, 2001)

The innate immunity relies on Pattern Recognition Receptors PRRs which help the immune cells like the phagocytes, macrophages, mast cells, neutrophils, eosinophils, Natural killer cells and dendritic cells to detect and respond to pathogens.

Generally the immune system responds to a pathogen in the following steps:

1. The pathogen is recognised by the cells of the innate immune. This triggers the release of cytokines, activation of the complement system and phagocytes that engulf the pathogen.
2. An acute inflammatory response is triggered by the innate system to contain the pathogen and helping migration of immunological cells.
3. The T helper cells are activated by PRRs that present the antigen.
4. The CD4+ T helper cells trigger an immune response by activating the B cells that produces antibodies against the pathogen and cytotoxic CD8+ T cells that eliminate any infected cells.
5. The pathogen is cleared from the system.