Q.How does chemical mediators act as physiological barriers ?

Swelling caused by tissue infection is the inflammatory response, a hallmark of innate immunity.

Inflammation is the body's rapid, non-specific (innate) response to tissue damage or infection. Damaged cells and immune cells release chemical mediators such as histamine and prostaglandins, which dilate local blood vessels (causing redness and heat) and increase their permeability, allowing plasma fluid and phagocytic white blood cells (neutrophils, macrophages) to move into the tissue -- the fluid accumulation and cell influx cause the visible swelling (oedema). Phagocytosis is the process of engulfing pathogens/debris by cells, and is part of, but not the same as, the swelling response itself. Mechani …

T-lymphocytes provide specific, acquired immunity - not innate immunity.

Innate immunity is the non-specific defence present from birth, comprising:

• Physical barriers: skin, mucus membranes.
• Physiological barriers: HCl in stomach, saliva, tears (contain lysozyme).
• Cellular barriers: neutrophils, macrophages, NK cells, and lymphoid organs like the spleen, which filters blood and traps pathogens.
• Cytokine barriers: interferons. …

(a) Phagocytes — the cellular component of innate (non-specific) immunity.

Innate immunity's cellular defence is provided mainly by phagocytic cells engulfing pathogens.

Innate (non-specific) immunity's cellular (as opposed to physical/physiological or chemical) barrier is provided chiefly by phagocytic cells — such as neutrophils, macrophages and monocytes — which engulf and destroy invading microbes through phagocytosis, without needing to specifically 'recognise' the pathogen the way adaptive immunity does. Antibodies, T-lymphocytes and B-ly …