2. For each of the following, identify the antibody or antibodies (if more than

Question

2. For each of the following, identify the antibody or antibodies (if more than one) that meet each of the following criteria. Briefly (about one sentence or less) answer the follow-up question a) Only antibody formed in the absence of TH-B cell interaction (T-independent pathway) What types of antigen allow this mechanism of B cell activation? What are three consequences of complement activation? What happens during ADCC? What is another opsonin that we talked about in Bio 221? b) Able to activate the complement cascade c) Able to initiate ADCC. Able to opsonize a pathogen e) f) g) h) Main antibody secreted across mucosal surfaces How do bacteria that use this portal of entry prevent this antibody from finding them? Used to prevent Rh- moms from being sensitized against an Rh+ baby. Briefly explain how this type of hypersensitive reaction could kill subsequent babies Found on the surface of a naïve B cell What is a "naïve" B cell? Responsible for the allergic response What happens during the two exposures required for the allergic response? (>1 sentence is OK) Used in artificial passive immunizations What is the difference between "active" and "passive" immunity? State some examples

Explanation / Answer

Q2) a)

- IgM is the only antibody formed in absence of Th-B cell interaction(T -independent pathway).

- Protein , polysaccharides and lipid antigens allow the mechanism of B cell activation.

Explanation- B-cells are activated by the binding of antigen to the receptors on their surface, as a result the cell divides and proliferates. Some stimulated B-cells become plasma cells, which secrete antibodies. Others become memory B-cells, which can be stimulated later to differentiate into plasma cells.

Q2)b) IgG and IgM antibody activates the complement cascade.

Explanation-Complement is a system of plasma proteins which can be activated directly by pathogens or indirectly by pathogen-bound antibodies, leading to a cascade or series of reactions taking place on the surface of pathogens. and eliminate them.

Complement activation causes three types of functions they are- phagocytosis, Inflammation,and Membrane attack.

Phagocytosis – by opsonizing the antigens (pathogen is marked for phagocytosis) . C3b cell shows high opsonizing activity.

Inflammation – function of inflammation is to eliminate the initial cause of cell injury, and do tissue repair  by bringing macrophages and neutrophils to that part .

Membrane attack – by rupturing the cell wall of bacteria the cell lysis occurs.

Q2)c)

IgG antibody able to initiate ADCC.

-ADCC or antibody-dependent cell-mediated cytotoxicity, is an immune mechanism in which Fc receptor-bearing effector cells recognize and kill antibody-coated target cells, expressing tumor- or pathogen-derived antigens on their surface. It is one of the mechanisms in which antibodies, act as part of the humoral immune response, to limit and control the infection

Q2)d) IgG is able to opsonize a pathogen.

IgE also able to opsonize a pathogen.

Q2)e) Ig A is the main antibody secreted across mucosal surface.

Bacteria turns their genes on and off to change their antigens. It prevents the immune system from making the correct antibodies to attack the pathogen. whe B-cells are activated, antibodies are produced. By this time, the pathogen has changed and the antibodies will not bind to the new antigens on the pathogen.This is called antigenic variation , used by bacteria to prevent the antibody from finding them.

Q2)f) anti-RhD IgG immunoglobulin injection is given to prevent mothers from being sensitized against Rh+ve baby at 28 weeks gestation.

During pregnancy if mother is Rh-ve and baby is Rh+ve, there will be usually no problem in the first pregnancy,as blood of mother and baby do not mix till delivery, but a small amount of the baby's blood can enter the mother's circulation, than the mother starts producing antibodies ( IgG) against the rhesus D antigen on her baby's red blood cells. During subsequent pregnancies the IgG can pass by the placenta into the fetus and if the level of it is sufficient, it causes destruction of rhesus D positive fetal red blood cells leading to Rh disease. and the baby dies.

Q2) g) Ig M is primarily found on naive B cells and latter IgG antibody found .

A naive B cell is a B cell that is not exposed to an antigen. Once exposed to an antigen, the naive B cell either becomes a memory B cell or a plasma cell

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