Q.(a) Explain how innate immunity protects our body against diseases. OR

(a) Innate immunity uses physical, physiological, cellular and cytokine barriers to give the body immediate, non-specific protection. (b) PCR amplifies a target DNA sequence millions of times through repeated denaturation-annealing-extension cycles using Taq polymerase.

(a) Innate (non-specific) immunity is the immunity present in an individual from birth and provides an immediate, general defence against any pathogen, without needing prior exposure. It operates through four categories of barriers. Physical barriers include the skin, which forms a mechanical barrier against microbial entry, and mucous membranes lining the respiratory, gastrointestinal, and urogenital tracts, which trap pathogens. Physiological barriers include the highly acidic environment of the stomach that kills most ingested microbes, and secretions such as saliva, tears, and nasal mucus, which contain the enzyme lysozyme that destroys bacterial cell walls. Cellular barriers involve various white blood cells, including neutrophils, monocytes/macrophages (phagocytic cells that engulf and digest pathogens) and natural killer (NK) cells (which destroy virus-infected and tumour cells). Cytokine barriers involve virus-infected cells producing signalling proteins called interferons, which diffuse to and protect neighbouring, as-yet-uninfected cells from viral infection by inducing an antiviral state. Together these barriers act rapidly, often within minutes to hours, to prevent and limit infection before the slower, specific (adaptive) immune response develops.

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