Immunology (H)
A. multiple choice questions (2? × 25 )
BBBDD CECDA CCCAD DBACA DADAC B. explain terms (6?× 5)
1.“Adaptive immunity” is provided by T & B lymphocytes（1?）. It is the 2nd line of defense. (1?) It has two important characteristics: Immune response is highly specific for the antigen that triggered it and has memory to the antigen. Exposure to antigen creates an immunologic “memory.”(3?) 2.Complement:
The complement system is an important component of innate immunity(2?). Complement was 1st described in 1890s as a heat-labile component of normal plasma, that augments opsonization of bacteria by antibodies and allows some antibodies to kill bacteria(1?). Complement is a group of proteins that form the principal effector arm of the humoral immune system(1?). It can be activated by the classical and alternative pathways, both pathways will eventually lead to the lytic pathway which featured by the formation of MAC(2?).
3.TCR T cell receptor(1?). T cell receptor is similar in structure to Immunoglobulins (similar to a single Fab fragment(2?). Composed of two glycoprotein chains (?/? or ?/?)(1?). Most mature T cells have TCRs composed of an ? chain and a ? chain (they are called ?/? T cells). The function is to recognize MHC/peptide and then activate T cells. It is important for providing the 1st signal for T cell activation.(2?)
4.MHC major histocompatibility complex(2?)
It was identified that the histocompatibility (the ability to accept grafts from another individual)depended on the donor and recipient sharing the same MHC gene type(2?). It was proved then that the gene is a very large, containing more than 100 separate gene loci, but the molecules which determine graft rejection are a limited group termed class I and class II MHC genes that map near to each other on a single chromosome.(2?) That's where the term, major histocompatibility complex comes from.
5,Oncofetal antigens are thus not TSA nor is their present, (1?)even at high concentration, in the
serum diagnostic of cancer, because high levels can result from non-neoplastic diseases including chronic inflammation of the bowel or cirrhosis of the liver. (2?)However, the quantitation of these molecules in the serum can be used to evaluate the tumor burden and effectiveness of drug treatment.(2?)
D. C.big questions (10?×2 )
1. structure and functions of antibody.
Structure: (indication---H, L chains, V, C regions, CDRs, FRs)
The N-terminal end of Ig is characterized by sequence variability (V) in both the heavy and light chains, referred to as the VH and VL regions respectively. The rest of the molecule has a relatively constant (C) structure. (1?)The constant portion of the light chain is termed the CL region. The constant portion of the heavy chain is further divided into three structurally discrete regions: CH1, CH2 and CH3. These globular regions, which are stabilized by intrachain disulphide bonds, are referred to as ?domains?. The sites at which the antibody binds antigen are located in the variable domains. The hinge region is a segment of heavy chain between the CH1 and CH2 domains. Flexibility in this area permits the two antigen-binding sites to operate independently(2?). At the amino acid level, the variable region is comprised of three regions of extreme variability (hyervarible region). They are called complementarity-determining regions, or CDRs.(1?) Interspersed among the CDRs are framework regions (FRs) which are less variable and more evolutionarily conserved. At the three-dimensional level, the three CDRs of each chain converge to form a combining site which recognize the antigenic determinant (epitope) (1?). Functions: The role of antibody alone------neutralization(1?)
NEUTRALIZATION OF TOXINS AND VENOMS, OF VIRUSES AND BACTERIA PREVENT ATTACHMENT TO CELL RECEPTORS Role of antibody in complement activation(1?)
ACTIVATION OF COMPLEMENT – IgM (most effective) and most subclasses of IgG can activate complement.
Role of antibody with effector cells-----phagocytes, NK cells(1?)
OPSONIZATION – the promotion of phagocytosis of antigens by macrophages and neutrophils.
Protein molecules called Fc receptors (FcR), which bind the constant region of most classes of antibody are present on the surfaces of phagocytes.
ANTIBODY-DEPENDENT CELL-MEDIATED CYTOTOXICITY (ADCC) – The linking of antibody bound to target cells (virus infected cells, or some tumor cells) with FcR of natural killer cells (NK cells), neutrophils, macrophages,or eosinophils can result in killing of the target cell.(2?)
2. 2-signal theory for T cell activation
A popular model to explain the requirement of T cell activation is the two-signal hypothesis. (1?) T cells require co-stimulation for activation -- binding of the TCR to MHC/peptide (signal 1) is not enough to activate a T cell by itself.(3?)
B7 and other costimulatory molecules on an APC binds to CD28 and other costimlatory molecules on the T cell to deliver a co-stimulatory signal (signal 2)(2?).Activation by peptide/MHC-TCR binding plus a co-stimulatory signal leads to Interleukin-2 (IL-2) release and up-regulation of the IL-2 receptor on the T cell. IL-2 stimulates growth and proliferation of T cells. (2?)In the absence of costimulation, T cells that encounter antigens either fail to respond and die by apoptosis or enter a state of unresponsiveness called anergy.(2?)