Question

Which type of MHC class molecules is found on all nucleated cells and is used to communicate with cytotoxic T-lymphocytes? Which class is found only on APCs and is used to communicate with helper T-lymphocytes?

Where does a lymphocyte typically encounter an antigen for the first time?

Describe how both helper T-lymphocytes and cytotoxic T-lymphocytes are activated.

Is a separate APC required for B-lymphocyte activation, or is a B-lymphocyte able to serve the role of an APC?

What are the six major functions of antibodies? Which occur due to antigen-binding and which depend on the Fc region?

How does the secondary response differ from the primary response? What is the advantage of the secondary response?

Describe how both active and passive immunity can be acquired naturally and artificially.

Answer 1

MHC or major histocompatibility complexes are group of gene which encode for protein found on the surface of cells that help immune system to recognize foreign substance. In human it is also called human leucocyte antigen (HLA) system.
Q1. Class 1 MHC are present on all nucleated cells and recognized by cytotoxic CD8 cell. It consist of two polypeptide chain alpha (45 K DA) beta (12k DA)
Q2. Class II MHC presented in immunological cell such as dendritic cell, macrophages or B cell . they can activate CD4 T cells. α1,α2 and β chain
Class III MHC- products that include secreted proteins that have immune function. Eg complimentary system.
Q3. Lymphocyte encounter antigen in the lymphoid organ such as spleen. Antigen enter the body and it is bound to antigen presenting cells such as dendritic cells(innate immune system). dentric cells bring the antigen to lymphoid organ which activate T lymphocyte(adaptive immune system).
Q4. Activation of T cells- T helper cells do not directly kill the cells like cytotoxic T cells.
T helper cells become activated by interacting with antigen presenting cells(APC) such as macrophages. APC ingest a microbe , they presented association with class II MHC molecule. This complex bind to T cell surface receptor.a second signal also required which obtained either by stimulation by cytokine or costimulatory reaction between B7 and CD 28. If two signals are received t cell become activated and get proliferated.
Activation of B cell- it require stimulation by a activated T helper cell. Activation is carried out through cell to cell interaction between CD40 ligand on T cell and CD 40 on B cell.
Q5.no activated t cell activate b cell. B cell in addition to antigen production , express high level of MHC class II can present antigen to CD 4 cell