Question

1. Mature B cells require particular receptors to be engaged by ligand to stimulate these cells to become antibody-secreting cells. Fill-in the table below with the receptor(s) on naïve B cells that transmit each signal and the corresponding ligand(s) that engage that receptor. (6 pts)

	Receptor(s) on B cell	Ligand(s)	Location in body where receptor engagement occurs
Signal 1
Signal 2

b. Briefly describe what happens to mature B cells that receive Signal 1, but not Signal 2? (2 pts)

2. For each description (a-h), circle all of the relevant types of hypersensitivities. (8 pts)

a. caused by an accumulation of soluble Ag-Ab complexes-------- Type I II III IV noneb. a TB skin test is based on --------------------- --------------------------Type I II III IV nonec. mast cell-mediated ----------------------------------------------------------- Type I II III IV noned. triggered by membrane-bound Ags ------------------------------------ Type I II III IV nonee. triggered by self Ags---------------------------------------------------------Type I II III IV nonef. transplant rejection---------------------------------------------------------- Type I II III IV noneg. Ab-mediated-------------------------------------------------------------------Type I II III IV noneh. more common in HIV patients---------------------------------------------Type I II III IV none

3. Naïve T cells require two distinct chemical signals to become activated. Fill-in the table with the appropriate: receptor on the naïve T cell, the ligand engaging the receptor and the cell source of the ligand. (10 pts)

b. Briefly describe the role of Signal 3 for CD4 T cells? b) In general, what type of receptors and ligand mediate Signal 3?

	Receptor(s) on T cell	Ligand(s)	Cell that provides ligand(s)
Signal 1
Signal 2

4. Briefly describe three (3) distinct mechanisms utilized by the immune system that normally function to prevent responses to self-antigens. (6 pts)

4b. Briefly describe three (3) different mechanisms by which normal immune tolerance mechanisms are thought to be broken, resulting in autoimmune responses. (6 pts)

5. For each description, circle all appropriate cell types: TH1 TH2 TH17 TFH Treg CTL (6 pts)

a. secretes cytokines that act to recruit neutrophils to sites of infectionb. promotes killing of intracellular pathogens by macrophages
c. secretes cytokines that suppress other T cell effectors
d. secretes cytokines that promote anti-helminth immunity

Answer 1

ANS 1 a - The surface immunoglobulin that serves as the B-cell antigen receptor (BCR) has two roles in B-cell activation. First, like the antigen receptor on T cells, it transmits signals directly to the cell's interior when it binds antigen. Second, the B-cell antigen receptor delivers the antigen to intracellular sites where it is degraded and returned to the B-cell surface as peptides bound to MHC class II molecules. The peptide:MHC class II complex can be recognized by antigen-specific armed helper T cells, stimulating them to make proteins that, in turn, cause the B cell to proliferate and its progeny to differentiate into antibody-secreting cells. Some microbial antigens can activate B cells directly in the absence of T-cell help. The ability of B cells to respond directly to these antigens provides a rapid response to many important bacterial pathogens. However, somatic hypermutation and switching to certain immunoglobulin isotypes depend on the interaction of antigen-stimulated B cells with helper T cells and other cells in the peripheral lymphoid organs. Antibodies induced by microbial antigens alone are therefore less variable and less functionally versatile than those induced with T-cell help.

On the basis of it we can fill the details in given table in question no 1.

Ans 1 b- Signal 2 is thought to amplify the intracellular signaling process triggered by signal 1. If a mature B cell receives signal 1 without signal 2, it may undergo apoptosis or become altered so that it can no longer be activated, even if it later receives both signals. This is one mechanism by which a B cell can become tolerant to self antigens.

Ans 2 a - Hypersensitivity type III

Ans 2 b - The tuberculin test or PPD (purified protein derivative) test are other names for the tuberculosis skin test. The tuberculin skin test is based on the fact that infection with M. tuberculosis bacterium produces a delayed-type hypersensitivity skin reaction to certain components of the bacterium.

Ans 2 c - Type IV

Ans 2 d- Type II

Ans 2 e - Type II

Ans 2 f - Type II

Ans 2 g- Type II

Ans 2 h- Type II

Ans 3 - This answer is also based on answer Answr 1A simultaneously.

Ans 3 b - Immune cells are the primary target of HIV infection. T-cells are a subset of white blood cells that play an important role in the body's immune system. CD4 is, by contrast, a type of protein found on the certain immune cells like T-cells, macrophages, and monocytes.

Ans 3 c - In general, Cell-surface receptors bind to an external ligand molecule and convert an extracellular signal into an intracellular signal. Three general categories of cell-surface receptors include: ion -channel, G- protein, and enzyme -linked protein receptors.

Ans 4 a- I).T Cells Are Subject to Positive and Negative Selection in the Thymus
T cells derive their name from the location of their production — the thymus, a small organ situated just above the heart. Examination of the developmental pathways leading to the production of mature cytotoxic and helper T cells reveals the selection mechanisms that are crucial for distinguishing self from nonself. These selection criteria are quite stringent; approximately 98% of the thymocytes, the precursors of T cells, die before the completion of the maturation process.

II). Autoimmune Diseases Result from the Generation of Immune Responses Against Self-Antigens
Image caduceus.jpg Although thymic selection is remarkably efficient in suppressing the immune response to self-antigens, failures do occur. Such failures results in autoimmune diseases. These diseases include relatively common illnesses such as insulin-dependent diabetes mellitus, multiple sclerosis, and rheumatoid arthritis. In these illnesses, immune responses against self-antigens result in damage to selective tissues that express the antigen.

III). The Immune System Plays a Role in Cancer Prevention
Image caduceus.jpg The development of immune responses against proteins encoded by our own genomes can be beneficial under some circumstances. Cancer cells have undergone significant changes that often result in the expression of proteins that are not normally expressed. For example, the mutation of genes can generate proteins that do not correspond in amino acid sequence to any normal protein. Such proteins may be recognized as foreign, and an immune response will be generated specifically against the cancer cell.

Ans 5 a- Secretes cytokines that act to recruit neutrophils to sites of infectionb. promotes killing of intracellular pathogens by macrophages may be TH1 TH2 TH17 TFH Treg CTL.

Ans 5 b - TH1 cells.

Ans5 c- T Helper 17 cells or TH17.

Ans 5 d - T Helper 2 cell or TH2.