Quick questions on Innate immune response in animals, first and second lines of defence: HSC Biology Module 7

The first line prevents pathogens from entering the body. It is always active and requires no recognition.

If a pathogen breaches the first line, the second line activates within minutes to hours. It is still non-specific but now involves cells and signalling molecules.

Inflammation is the most visible part of the innate response. It has four cardinal signs: heat, redness, swelling and pain.

- Skin. A multilayered keratinised epidermis is the largest barrier. Continuous shedding of skin cells removes attached pathogens. - Mucous membranes line the respiratory, digestive, urogenital and conjunctival tracts.

- Stomach acid (pH around 2) kills most ingested pathogens. - Lysozyme in tears, saliva and sweat digests bacterial cell walls. - Sebum on skin lowers pH and contains antimicrobial fatty acids.

- The normal microbiota on skin and in the gut outcompetes invading pathogens for nutrients and attachment sites.

- Neutrophils are the first responders. They migrate to the site within minutes and engulf pathogens. - Macrophages arrive later and have higher capacity.

Lymphocytes that recognise virus-infected and cancerous cells by their reduced MHC class I expression. They release perforin (forms pores in membranes) and granzymes (induce apoptosis).

A cascade of around 30 plasma proteins that: - Mark pathogens for phagocytosis (opsonisation). - Recruit phagocytes (chemotaxis). - Form a membrane attack complex (MAC) that lyses pathogen membranes.

Cytokines released by virus-infected cells that signal neighbouring cells to enter an antiviral state, slowing viral spread.

1. Tissue damage. Pathogens or wounding trigger damaged cells and mast cells to release histamine, prostaglandins and bradykinin. 2.

Damaged cells and mast cells released histamine, causing vasodilation (redness, heat) and increased capillary permeability (swelling). Pain came from stretched tissue and prostaglandin sensitisation of pain receptors. Neutrophils migrated to the wound by chemotaxis and phagocytosed any bacteria entering through the cut.

Innate is fast (minutes to hours), non-specific, and lacks memory. Adaptive is slow (days), specific to one antigen, and produces memory cells.

Markers expect histamine (the main vasodilator), prostaglandins (pain), and cytokines (signalling).

NK cells are innate, recognising reduced MHC. Cytotoxic T cells are adaptive, recognising specific antigens on MHC class I.