Tag: immunity

Clonal selection is a process to determine how B or T cell recognizes an antigen that enters the body is selected from the per-existing cell pool of differing antigen specificities and its proliferation to generate a clonal cell population that eliminates the antigen.
Thus, the correct answer is option B.

The thymus is the primary lymphoid organ where lymphocytes originate and/or mature. T-lymphocytes originate from lymphoid progenitor cells in thymus via three developmental stages, namely pro, pre and immature T cells. The immature T cells mature in thymus only. B cell originates and matures in red bone marrow, fibrinogen is the clotting factor 1 in blood and phagocytes are the type of WBC. Thus, the correct answer is E.

Phagocytes are the component of the non specific immune response. The encounter of B cell with a specific antigen activates its clonal expansion which in turn gives rise to plasma cell and memory cells.  A plasma cell is a mature B cell that serves in mass production of antibodies against a specific antigen. Pathogens are the disease-causing organisms that carry antigens. Fibrinogen is involved in the clotting process. T cells are responsible for cell-mediated immunity. Thus, the correct answer is A.

The endogenous pathway is used to present cellular peptide fragments broken down by proteosomes on the cell surface of MHC class I molecules. Transporter associated with antigen processing spans the membrane of the rough endoplasmic reticulum and transports the peptides into the lumen of the rough endoplasmic reticulum. Once the peptide is transported into the ER lumen it binds to the cleft of the MHC class I molecule, stabilizing it and allowing it to be transported to the cell surface by the Golgi apparatus. Thus the correct answer is option B.

Major histocompatibility complex (MHC) are the proteins on the surface of cell membrane. These proteins play an important role in the recognition of the foreign antigens. There are two MHC complexes called as MHC-I and MHC-II complex. These complexes play a different role in different processes. The genes for MHC complex are located on the chromosome 6 in the case of humans. In the case of mice, these genes are on chromosome 17. 

MHC class II molecules bind peptides from antigens processed in organelles. These extracellular antigens, such as whole bacteria, engulfed by APCs via phagocytosis or endocytosis are enclosed in an intracellular vesicle. This vesicle containing peptides is fused with another vesicle containing MHC class II proteins. Upon fusion, the peptide is loaded onto MHC class II molecules, and the entire complex migrates to the cell membrane surface, where peptide-specific CD4 T cells recognize it. Thus the correct answer is option A.

• A T cell, or T lymphocyte, is a type of lymphocyte that plays a central role in cell-mediated immunity. T cells can be distinguished from other lymphocytes, such as B cells and natural killer cells, by the presence of a T-cell receptor on the cell surface. They are called T cells because they mature in the thymus. 
• The types of T-cells are killer cells (cytotoxic cells) which destroy virus-infected cells and tumor cells, and are also implicated in transplant rejection, helper T-cells which  assist other white blood cells in immunologic processes, including maturation of B cells into plasma cells and memory B cells, and activation of cytotoxic T cells and macrophages and suppressor T-cells which are crucial for the maintenance of immunological tolerance.