Blood, Lymph & Immunity

Circulation. Surveillance. Coordination.

Blood and lymph connect tissues with immune organs, transport cells and signals, and help protective responses reach the right place. The two networks work together but follow different routes.

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Two networks, one coordinated defense

The blood and lymphatic systems connect tissues, distribute signals and enable immune-cell movement. Each has distinctive transport and surveillance roles.

Blood: the transport network

Plasma carries antibodies, complement and signaling proteins. Leukocytes circulate and can enter tissues when recruited. Red blood cells carry oxygen, while platelets support hemostasis and interact with immune responses.

Red cells, leukocyte and platelets within a blood vessel

Red cells: oxygen transportWhite cells: immune defensePlatelets: hemostasisPlasma: soluble proteins

Lymph: the tissue connection

Lymphatic capillaries collect interstitial fluid and carry antigens and migrating immune cells toward draining lymph nodes. Collecting vessels and valves direct flow; lymph ultimately returns to the bloodstream.

Lymphatic drainage from tissue toward a node

Tissue fluid → lymphatic capillaryAntigens and migrating cells → draining nodeCollecting lymph → return to blood

Lymph nodes: meeting places for immunity

Lymph node with cortex, paracortex and medulla

Migratory dendritic cells bring tissue-derived antigens to lymph nodes. Many naive T and B cells enter from blood through specialized venules, then encounter antigen in organized compartments.

B-cell follicles
Outer cortical regions support B-cell interactions.
T-cell zone
The paracortex supports T-cell and dendritic-cell encounters.
Afferent and efferent lymph
Afferent vessels enter; efferent lymph exits at the hilum.

Lymph nodes filter lymph. The spleen monitors blood.

How the systems work together

1. Detect

Tissue immune cells recognize local signals.

2. Deliver

Lymph transports antigens and migrating cells toward nodes.

3. Activate

Antigen recognition and supporting signals activate lymphocytes.

4. Respond

Effector cells can return to circulation and reach affected tissues.

Activated B cells can become antibody-secreting plasma cells; selected lymphocytes become memory cells.

Health and disease

Infection & inflammation

Cell trafficking helps direct protective responses toward affected tissues.

Lymphedema

Impaired lymph drainage can cause persistent swelling and tissue changes.

Cancer

Lymphatic pathways support immune responses but can also provide routes for tumor spread.

Blood, Lymph & Immune Aging

Age-related changes can affect immune-cell trafficking and communication.

Changing lymph nodes
Stromal organization and cellular interactions can alter with age.
Changing immune responses
These shifts can influence responses to newly encountered antigens.
Evidence in context
Human and animal studies provide complementary findings. Effects vary between tissues and people.

TakeawayEffective immunity depends on where cells travel—and where they meet.

Selected sources and references

Artwork illustrates the main mechanisms schematically; molecular sizes, colors and distances are not literal.