question_answer

(i) How are the following involved in protecting human body from invading pathogens?

(a) Lymph nodes

(b) Plasma cells

(c) Cytotoxic T - cells

(ii) Why secretion of IgE antibodies and histamine is not beneficial for humans during allergy?

Or

HIV (retrovirus) does not follow central dogma, then how does it replicates inside the host cell? Explain with diagram.

Answer:

(i) (a) Lymph nodes are small structures present at different sites along the lymphatic system. They trap microorganisms and other antigens that enter the lymph and tissue fluid. Antigens trapped in the lymph nodes activate the lymphocytes and produce an immune response.

(b) Plasma cells are formed by the division and differentiation of activated B-cells. A few days after an exposure to an antigen, a plasma cell secretes millions of antibodies for about 4-5 days, until the plasma cell dies.

(c) Cytotoxic T-cells are responsible for providing cell-mediated immunity. An activated cytotoxic T-cell is specific to a target cell that has been infected and kill the target cell by preventing the completion of life cycle of the pathogen. These cells can also kill the cancer cells.

(ii) Allergy mainly involves the release of IgE antibodies and histamine. It causes marked dilation of peripheral blood vessels and capillaries due to which they become highly permeable. It results in the large amount of fluid leakage out of the blood into tissue.

The blood pressure increases drastically, that may result in the death of individual within a short time.

Or

Life Cycle of HIV

HIV does not follow central dogma. It follows reverse central dogma. Its life cycle and replication process is given below

(i) Virus enters macrophage after entering body of the person.

(ii) RNA genome replicates to from viral DNA by enzyme reverse transcriptase.

(iii) Viral DNA gets incorporated into the host cell DNA and directs the infected cells to produce new viruses.

(iv) Virus particles enter into helper T-lymphocytes\[({{T}_{H}}cells)\]in the blood and continue to replicate and produce viral progenies.

(v) Number of helper T-lymphocytes progressively decreases in the body of the infected person.

(vi) The person experiences periods of fever, diarrhea and weight loss during this period.

(vii) As the number of T-cell decreases, the immunity also decreases. As a result, affected individual cannot produce any immune response even against common bacteria like mycobacterium, parasite like Toxoplasma, viruses and fungi.