Immune Response medical comic

This comic shows how the immune system organises a coordinated defence. It follows antigens through the two presentation pathways, the signals that switch on helper T cells, the killing work of cytotoxic T cells and NK cells, B-cell activation and germinal centres, antibody effector functions, mucosal immunity and how responses are measured in the lab.

For MBBS, NEET-PG, FMGE, NEXT and USMLE revision.

The immune response: what the comic covers

High-yield points

• Internal (cytosolic) antigens are presented on MHC class I to CD8+ T cells; external antigens taken up by APCs are presented on MHC class II to CD4+ T cells.
• Professional antigen-presenting cells are dendritic cells, macrophages and B cells; dendritic cells are the most potent at starting a primary response.
• Helper T-cell activation needs antigen on MHC plus co-stimulation (B7 to CD28) and cytokines; IL-2 then drives the cell's own proliferation.
• Activated helper T cells branch into subsets such as Th1 (cell-mediated immunity) and Th2 (antibody and allergy responses), and leave memory cells behind.
• Cytotoxic T lymphocytes kill infected or abnormal cells through perforin, granzymes and Fas ligand.
• NK cells kill cells that lack MHC class I, and also kill antibody-coated cells by ADCC.
• B cells can be activated with T-cell help (giving class switching, affinity maturation and memory in germinal centres) or without it by repetitive antigens.
• Secretory IgA is moved across mucosal cells by transcytosis to guard mucosal surfaces.

Quick questions

What is the difference between MHC class I and class II presentation?

MHC class I shows peptides from inside the cell, such as viral proteins, to CD8+ cytotoxic T cells, and is on almost all nucleated cells. MHC class II shows peptides from ingested material to CD4+ helper T cells, and is mainly on antigen-presenting cells.

Why do T cells need two signals to activate?

Antigen on MHC alone (signal 1) can make the T cell unresponsive (anergic). Co-stimulation, such as B7 on the APC binding CD28 on the T cell (signal 2), plus cytokines, is needed for full activation. This protects against autoimmunity.

What happens in a germinal centre?

Activated B cells multiply, undergo somatic hypermutation and class switching, and are selected for high-affinity binding, producing plasma cells and memory B cells.

Is this comic free to read?

The first pages are free to preview. Members read the full comic, and you can sign up free to read one comic in full.

Read next

• Components of the Immune System medical comic
• Innate and Acquired Immunity medical comic
• Antigens medical comic
• Tumour Immunology medical comic

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