Question

QUESTION 6 Select the INCORRECT pairs. Histamine, bradykinin, leukotrienes do not cause constracction of smooth muscles. Immune complex mediated hypersensitivity - Type III hypersensitivity graft rejection - example of type IV hypersensitivity Type IV - T cell or delayed hypersensitivity The tuberculin or PPD test is an example of Type Ill hypersensitivity reaction. Type 1 hypersensitivity - Involves IgE and is immediate. Example is anaphylaxis.

Answer 1

Question-6

The incorrect pairs are- Histamine, bradykinin, leukotrienes do not cause contraction of smooth muscles (These are activators involved in hypersensitivity reactions. They act mainly by causing vasodilation and smooth muscle contraction).

The tuberculin or PPD test is an example of type III hypersensitivity reaction. (Tuberculin test is an example of type IV hypersensitivity reaction, which is a delayed type reaction. It is used to determine, whether, a person is infected with Mycobacterium tuberculosis. In this test, bacterial protein, PPD, is injected intradermally. If the person has tuberculosis (that is, if bacterial antigen is present), a red, swollen lesion will develop at the site of injection, within 48-72 hours. During initial infection, the bacterial antigen within the body sensitizes and activates T_H cells. This sensitization needs a period of 1-2 weeks. These T_H cells are involved in the development of delayed type hypersensitivity (DTH). Subsequent exposure with the same antigen, for example during tuberculin test, leads to the release of a variety of cytokines, which recruits and activates macrophages. This response takes a period of 48-72 hours. This amount of time is needed by the cytokines to get secreted and activate and bring macrophages to the site of infection).

Question-7

Exotoxins are made up of proteins. (Toxins are classified into exotoxins and endotoxins. Exotoxins are proteinaceous in nature, which is released by a bacteria into the surrounding medium. On the other hand, endotoxins are lipids, which are part of the outer membrane of gram negative cell wall).

Exotoxins are released from live cells. (Exotoxins are produced as a part of bacterial metabolism. They are released into the surrounding by live cells. On the other hand, endotoxins are a part of bacterial outer membrane. Being an integral part of the cell, they can only be released after cell lysis).

Exotoxins can be denatured by heat. (Since, exotoxins are proteins, they can be denatured by heat (heat-labile). On the other hand, endotoxins are lipid molecules, and hence, are heat-stable).

Thus, the 2nd, 4th and 6th options will be true.

Question-8

All of the given pairs are correct.

(Type III hypersensitivity occurs due to accumulation of immune complexes. When large amount of immune complexes are deposited at sites, such as, joints, blood vessels, glomerular basement membrane of kidney, etc, the complement system is activated. Anaphylatoxins released due to complement activation, causes mast cell degranulation, and recruits neutrophils to the site. This results in localized tissue damage due to lytic enzymes secreted by neutrophils and activation of membrane attack complex. Thus, type III hypersensitivity occurs due to formation and accumulation of immune complex.

Type IV hypersensitivity shows delayed type response. The delay is due to the time taken by the cytokines to get released and further recruitment and activation of macrophages to the site of infection, during secondary exposure to the same antigen. Thus, the unique characteristic of type IV hypersensitivity is that, the results are not immediate. They are seen after a period of 48-72 hours.

Type II hypersensitivity is mediated by antibodies. It is mostly seen during blood transfusion reactions, when the blood given to the recipient, does not match with the recipient's blood group. This results in destruction of the transfused blood cells by antibodies, such as IgM and IgG. Thus, type II hypersensitivity is initiated by antibodies, that is, this type of hypersensitivity is antibody mediated.

Type I hypersensitivity is initiated by allergens. When an allergens enters the body, humoral immunity is activated, which results in the production of IgE immunoglobulins. Allergen bound IgE sensitizes mast cells and basophils. A second exposure to the same allergen causes degranulaion of the sensitized mast cells and basophils, which causes vasodilation and smooth muscle contraction. The effects are seen immediately. Hence, type I hypersensitivity is known as immediate hypersensitivity).