INNATE IMMUNITY

Innate immunity is the immunity we are born with and is the first line of defense. It is nonspecific in nature meaning it protects you from all antigens. Innate immunity acts as a barrier that keeps harmful antigens or pathogens from entering the body. There are three types of defensive mechanisms in innate immunity which are:

(i) Barriers; anatomic, physiologic, 

(ii) phagocytosis, and 

(iii) induced response

Anatomical Barrier

The anatomical barrier includes the skin and the surface of mucous membranes. The skin and the mucous membrane block the entry of most microorganisms. skin consists of two distinct layers: the outer layer- epidermis and a thicker inner layer- dermis. Our epidermis protects our body from ultraviolet (UV) radiation, pathogens (bacteria, viruses, fungi and parasites) and chemicals, and the keratin protein present in the epidermis keeps our body hydrated. The sebaceous glands (present with the hair follicles) in the dermis produce sebum which is oily in nature and maintains the pH of the skin between 3 and 5 making it acidic. This acidic pH prevents the growth of most microorganisms. So the entry of pathogens will occur only if there is break in the skin. Break in skin may occur due to injury or by biting of insects (e.g., protozoan that causes malaria, enters humans when mosquitoes bite them).

The internal organs like the gastrointestinal tract, respiratory, and urinary and reproductive tracts are lined by mucous membranes, The epithelial cells of the mucous membrane secrete mucous which not only traps microorganisms it also has antibacterial and antiviral properties.

Physiological Barriers  

The physiological barriers means keeping the pathogens separated by functional parameters like temperature, pH, and various soluble and cell associated molecules of the body. Normal body temperature inhibits growth of some pathogens (see margin remark). When we are infected, we get fever, this increase in temperature also helps in inhibiting the growth of some pathogens. The pH in the stomach is 2.0, this highly acidic pH kills the pathogen and acts as a barrier. Lysozyme, a hydrolytic enzyme found in mucous secretions and in tears, saliva kills the pathogens by hydrolysing their cell wall. In the eye and urinary tract there is rapid flow of secretions. The rapid flow of secretions causes constant washing and flushing which makes it difficult for microbes to enter these routes. Upon breach of the above barriers by pathogens and their invasion into the tissue, they are recognised by several receptors which trigger an immune response like phagocytosis and induced responses

Chickens, have innate immunity to anthrax because their high body temperature inhibits the growth of the bacteria.

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