Major Histocompatibility Complex (MHC) Overview

MHC molecules are like cellular billboards that display fragments of proteins (antigens) to immune cells. They are crucial for the immune system to recognize and respond to foreign invaders.

MHC Class I molecules are found on all nucleated cells in the body. They present fragments of proteins from inside the cell, like viral proteins, to Cytotoxic T-cells (CD8+ T-cells).

MHC Class II molecules are found on professional antigen-presenting cells (APCs) like macrophages, dendritic cells, and B-cells. They display fragments of engulfed pathogens to Helper T-cells (CD4+ T-cells).

Antigen-Presenting Cells (APCs) are the 'show and tell' masters of the immune system. They capture and process antigens, displaying them to T-cells to initiate a response.

Dendritic Cells are the most potent APCs. They patrol tissues, engulf antigens, and travel to lymph nodes to present them to naïve T-cells.

Macrophages are 'cellular vacuum cleaners' that engulf and destroy pathogens. They then process and present antigens via MHC Class II to Helper T-cells.

B-cells are specialized lymphocytes that recognize specific antigens and produce antibodies to fight them. They also act as APCs, presenting antigens to Helper T-cells for activation.

Helper T-cells (CD4+ T-cells) are essential for orchestrating the immune response. They are activated by antigens presented on MHC Class II molecules and then release cytokines to activate other immune cells.

These cells are activated by antigens presented on MHC Class I molecules and kill infected or cancerous cells by releasing perforin, which punches holes in the cell membrane, and granzymes, which trigger apoptosis (programmed cell death).

These lymphocytes, unlike T-cells, do not rely on MHC for activation and target cells that have downregulated MHC Class I to evade detection. They kill by releasing perforin and granzymes, similar to cytotoxic T-cells.

A group of proteins that act as messengers between immune cells, ensuring a coordinated defense. Key examples include interleukins, interferons, and tumor necrosis factor.

A group of proteins in the blood that tag pathogens for destruction, form a membrane attack complex (MAC) that punctures the pathogen's membrane, and enhance inflammation to attract more immune cells.

These cells engulf pathogens and break them down into antigens, which are displayed on MHC Class II molecules. They act as antigen-presenting cells (APCs) to activate helper T-cells.

These cells recognize antigens via their T-cell receptor (TCR) and become activated. They release cytokines to recruit and activate B-cells, cytotoxic T-cells, and macrophages.

These cells are stimulated by antigens presented on MHC Class II molecules and produce antibodies, which bind to pathogens and neutralize them.

These cells suppress overactive immune responses to prevent damage to the body's own tissues, acting as a regulator to maintain immune homeostasis.