Question

  Antigen presentation is an important link between innate and acquired (adaptive) immunity. Explain in detail how the process occurs. Please include: what cells might be involved, the differences between MHC 1 and MHC 2 and how antigen presentation leads to differential activation of acquired immunity.

Answer 1

Answer: Link between innate and acquired immunity: Innate immunity involve cells like neutrophils, macrophages, dendritic cells and natural killer cells. Once the body encounter with the antigen macrophages and dendritic cells the phagocytic cells engluf the antigen via endocytosis and process it in the endosome. After processing Macrophages and dendritic cell present these antigen onto the cell surface via MHC1 and MHC2 (cell surface receptor). Macrophage and Dendritic cells are antigen presentimg cells. These cells present antigen and T lymphocytes cells ( cells of acquired immunity) recoganise the MHC presenting antigen and become activated. Activated T cells release cytokines and interleukins. These activted Tcells proliferate and form T helper cells T cytotoxic cells. T helper and T cytotoxic cells help in antigen neutralization and memory cell formation.

Difference between MHC 1 amd MHC 2:

MHC 1 MHC 2

1. Two polypeptide chains are present alpha and beta2 microglobin. Alpha chain is integral membrane protein and beta2 is pheriphral protein.	1. Two polypeptide chain alpha and beta are present. both are integral membrane ptotein.
2. Genes for MHC1 present on chromosome no. 6 and 15.1`	2. Genes for MHC2 present on chromosome no. 6.
3. MHC1 is non specific. All nucleated cells express MHC1.	3. MHC2 mainly present on macrophage, B-lymphocytes and dendritic cell.
4. Alpha chain forms the antigen presenting site.	4. Alpha and Beta both subunits form the antigen presenting site.
5. only 8-10 amino acids long peptide can binds to MHC1.	5. 13-18 amino acid long peptide can binds to MHC2.

Antigen presented by MHC1 : Antigen presented by MHC1 is recoganised by T helper cells. After neutralization of antigen T helper cells give rise memory cells.

Antigen presented by MHC2: Antigen presented by MHC2 is recoganised by T cytotoxic cells. These cells secretes perforin and granzymes. No memory cells are formed.