Question

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? b)________ Able to activate the complement cascade. What are three consequences of complement activation?

c)________ Able to initiate ADCC. What happens during ADCC?

d)________ Able to opsonize a pathogen. What is another opsonin that we talked about in Bio 221?

e)________ Main antibody secreted across mucosal surfaces. How do bacteria that use this portal of entry prevent this antibody from finding them?

f)________ Used to prevent Rh- moms from being sensitized against an Rh+ baby. Briefly explain how this type of hypersensitive reaction could kill subsequent babies.

g)________ Found on the surface of a naïve B cell. What is a “naïve” B cell?

h)________ Responsible for the allergic response What happens during the two exposures required for the allergic response? (>1 sentence is OK)

i)________ Used in artificial passive immunizations What is the difference between “active” and “passive” immunity? State some examples.

Answer 1

a) The thymus-independent antibody is formed in the absence of TH-B cell interaction i.e. IgM. Helper T cells are required to activate B-cell, protein antigens and many microbial constituents, such as bacterial polysaccharides. These microbial antigens are known as thymus-independent or TI antigens.

b) IgG and IgM are able to activate the complement cascade. Complement is a system of plasma proteins that can be activated directly by pathogens or indirectly by the pathogen-bound antibody that are IgG and IgM.  

Three main consequences are i. Lysis of cells such as bacteria, allografts and tumor cells, ii) Generation of mediators that participate in inflammation and attract neutrophils iii) Opsonization ie. Enhancement of phagocytosis.

c) IgG is able to initiate ADCC. ADCC is triggered by the interaction of target?bound antibodies belonging to IgG or IgA or IgE classes on the effector cell surface. ADCC involving human IgG1, the most used IgG subclass for therapeutic antibodies, is highly dependent on the glycosylation. ADCC is the killing of an antibody?coated target cell by a cytotoxic effector cell through a nonphagocytic process.

d) IgG and IgE are able to opsonize a pathogen. Another opsonin is attaching antigens to phagocytes.

The process starts with  IgG, IgA, or IgM antibodies being made against a surface antigen of the organism or cell to be phagocytosed. The Fab portions of the antibody react with epitopes of the antigen and can then bind to receptors on neutrophils and macrophages thus sticking the antigen to the phagocyte.