Major Histocompatibility Complex (MHC)

 

Major Histocompatibility Complex (MHC)

1. *Definition*: A part of the genome that codes for molecules important in immune recognition.

2. *Function*: Recognizes foreign molecules, determines histocompatibility.

3. *MHC Proteins*: Cell surface proteins essential for acquired immune system.

4. *Role*: Binds to peptide antigens, displays them on cell surface for T-cell recognition.

Antigen-Presenting Cells (APCs)

1. *Definition*: Immune cells that process and present antigens for recognition by lymphocytes (T cells).

2. *Function*: Mediates cellular immune response.

3. *Types*: Heterogeneous group of immune cells.

Simple Analogy

          Think of MHC proteins like security guards at a checkpoint. They check the ID cards (peptide antigens) of everyone trying to enter (foreign molecules). If the ID card doesn't match, the security guard (MHC protein) raises an alarm, and the immune system sends T-cells to attack the foreign molecule.

 

T-Cell Receptors and Antigen Recognition

1. Recognition: T-cell receptors recognize antigens bound to MHC molecules.

2. MHC Molecules: Polymorphic glycoproteins on cell membranes.

3. Antigen Presentation: Recognition event where MHC molecules present antigens to T-cells.

MHC Molecules

1. *Class I MHC Molecules*

    - Recognized by TC (Cytotoxic T) cells.

    - Expressed by all nucleated cells

    - Consist of heavy chain + β2-microglobulin

2. *Class II MHC Molecules*

    -  Recognized by TH (Helper T) cells.

    - Expressed only by antigen-presenting cells (APCs)

    - Consist of α and β glycoprotein chains

    - APCs: Dendritic cells, macrophages, and B cells

T Cell Activation

1. *Naive T Cell*: Encounters antigen combined with MHC molecule

2. *Proliferation and Differentiation*: T cell proliferates and differentiates into

    - *Memory T Cells*

    - *Effector T Cells*

 

Class III MHC Genes

1. *Function*: Encode secreted proteins with immune functions.

2. *Examples*: Complement proteins, inflammatory molecules.

3. *Role*: Do not present antigenic peptides.

TCR Co-Receptors

1. *CD4*: Interacts with MHC Class II on APCs (Antigen-Presenting Cells).

2. *CD8*: Interacts with MHC Class I on all nucleated cells.

Key Interactions

1. *CD4 + MHC Class II*: Helper T cells (TH) recognize antigens.

2. *CD8 + MHC Class I*: Cytotoxic T cells (TC) recognize antigens.