Immunity and Host defence

Immune system is categorized into non-specific and specific response. Innate immunity is integral and is mobilized following the infection. Innate is termed non-specific because the protective response is the same regardless of the initiating infection. This is in contrast to the adaptive immune system which is slower, responds specifically, and generates an immunological memory.

The primary component of innate immunity is inflammation. Injured cells release cytokines and other pro-inflammatory factors like bradykinin, histamine, leukotriene, prostaglandins, and serotonin to contain the spread of infection and promote healing. These pro-inflammatory mediators induce vasodilatation and attract phagocytes. Neutrophils subsequently increase the response by attracting lymphocytes and leukocytes. Activation of the Complement cascade enhances the innate response.

An important consequence of complement cascade activation is opsonization. Opsonization of pathogenic antigens tags invasive microorganisms for ingestion and destruction by phagocytes. Though innate response involves a wide range of cell types but is mostly dependent on basophils, mast cell, neutrophils and macrophages. Another important function of the innate immune system is to stimulate the adaptive immune response via antigen presentation.