Question

1. What kind of cell is most likely to interact with a class I MHC protein on a cell surface?

2. The antibody-combining site binds to a part of the antigen that is complementary to the combining site. What is this portion of the antigen called?

3. Which T cell is most likely to be stimulated by the appearance of exogenous antigens presented by an antigen-presenting cell?

4. What properties of fibronectin and other similar molecules of the ECM allow them to fulfill their function of integrating the interactions between the ECM and cells?

Answer 1

1. T lymphocytes generally recognize antigens as a complex of short linear peptides bound to self-MHC molecules on the surfaces of Antigen Presenting Cells (APCs).The source of these peptides can be either extracellular or intracellular proteins and derived from either self or foreign molecules. CD8 T cells activated by MHC class I peptide complexes become cytotoxic and can kill the cells that present the pathogen-derived peptides.

2. Epitope is the site on the antigen that is recognised and bound by an antibody. It is normally about six amino acids or carbohydrate residues in size. The binding of antibody to the antigen takes place at the antigen determining site called paratope. Epitopes on protein antigens may not be continuous in structure. The epitope is also called as antigenic determinant

3. T- helper Lymphocytes recognise antigen on the cell surface of the antigen presenting cell and secrete cytokines which stimulate different mechanism of immunity and inflammation. Cytotoxic T lymphocytes recognize antigens in infected cells and kill these cells.

4. Fibronectin is a glycoprotein present in two forms of plasma and extracellular. The extracellular fibronectin serve to organise cellular interaction with extracellular matrix by binding to various compounds of extracellular matrix and to membrane bound fibronectin receptors on cell surfaces. Fibronectin plays an important role in embryogenesis and chondrogenesis. Cell adhere to the extracellular matrix through the cell adhesion proteins. The extracellular matrix is directly connected to the cells to which it surrounds. The important connectors are proteins called integrins, which are embedded in the plasma membrane. Proteins in the extracellular matrix, like the fibronectin molecules can act as bridges between integrins and other extracellular matrix proteins such as collagen. On the inner side of the membrane, the integrins are linked to the cytoskeleton.