Components of the Immune System medical comic

This comic draws the immune system as a planned city. It visits the central lymphoid organs where cells are born and trained, the peripheral organs where they meet antigen, and the cells that do the work, then explains MHC and cytokines and what goes wrong when parts of the system fail.

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

Components of the immune system: what the comic covers

High-yield points

Central (primary) lymphoid organs are the bone marrow and thymus; peripheral (secondary) organs include lymph nodes, spleen and mucosa-associated lymphoid tissue.
T cells mature in the thymus: the cortex is the zone of proliferation and positive selection; the medulla completes maturation, and central tolerance removes self-reactive cells.
The thymus is largest relative to body size in early life and involutes after puberty.
Lymph nodes have B-cell follicles with germinal centres in the cortex, T cells in the paracortex and plasma cells in the medulla.
The spleen's white pulp is lymphoid tissue; the red pulp removes old red cells; loss of the spleen raises the risk of infection with encapsulated bacteria.
NK cells kill without prior sensitisation; macrophages engulf and present antigen; dendritic cells are the best antigen-presenting cells; granulocytes are first responders.
MHC class I is on almost all nucleated cells, MHC class II on antigen-presenting cells; MHC genes sit on chromosome 6.
Cytokines are the messengers that coordinate immune cells.

Mnemonics from the comic

MHC matching: The rule of eight: MHC class × CD number = 8 (class I with CD8, class II with CD4).

Quick questions

What are the primary lymphoid organs?

The bone marrow, where blood cells form and B cells mature, and the thymus, where T cells mature and are selected.

Where do T and B cells sit in a lymph node?

B cells sit in the follicles of the outer cortex, where germinal centres form. T cells occupy the paracortex. Plasma cells collect in the medullary cords.

Why does losing the spleen raise infection risk?

The spleen filters blood and makes antibodies against polysaccharide capsules. Without it, people are at risk of overwhelming infection by encapsulated bacteria such as pneumococcus, Haemophilus influenzae type b and meningococcus.

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.