Immune responses: connect recognition to action

1. The phagocyte recognises and attaches to the target.
2. The cell surface encloses the target in a vesicle.
3. Lysosomes fuse with the target-containing vesicle.
4. Lysosomal enzymes digest susceptible target material.
5. Products of digestion can be processed or removed by the cell.

Recognition precedes enclosure. Lysosome fusion brings digestive enzymes into the compartment containing the target. Digestion occurs inside the phagocyte; antibodies may aid recognition but do not themselves engulf the target.

An antibody is a protein, not a cell with lysosomes.

1. The B cell presents antigen-derived material to a suitable activated helper T cell.
2. Matching recognition and helper signals support activation of the B cell.
3. The selected B cell divides to expand a clone with that specificity.
4. Some cells in the clone differentiate into plasma cells.
5. Plasma cells secrete antibodies with the relevant specificity.

The chain follows a selected T-dependent response, not all B-cell activation. Helper recognition/signalling supports clonal expansion and differentiation. Plasma cells secrete antibodies; other descendants can become memory cells.

The antigen selects cells with suitable receptors; it does not make every lymphocyte invent a new matching receptor.

Correct link: A matching T-cell receptor recognises the presentation, with the necessary activation signals.

Specific recognition plus the necessary signals can activate a helper T cell. Activated helper cells can support other responses through signalling. Receptor specificity matters; presentation is not an instruction for every T cell to respond identically.

Helper T cells support responses by signalling; they are not antibody-secreting plasma cells.

Correct link: Relevant memory cells persist and can respond on re-exposure.

Memory cells with relevant specificity may persist and contribute to faster expansion and effector activity on re-exposure. This does not guarantee complete protection against every infection.

Immune memory refers to cells and a changed response, not a permanent supply of identical antibodies.

An antibody binds a suitable antigen through its specific binding region. Bound antibodies can make a target easier for phagocytes to recognise; antibodies can also aggregate suitable targets. The phagocyte carries out enclosure and lysosomal digestion. Binding and digestion are performed by different components.

Do not say that antibodies are enzymes that directly digest all pathogens.

• The antibody binds a suitable antigen specifically.
• Binding can aid recognition or aggregation of targets.
• The phagocyte, rather than the antibody, performs engulfment and digestion.

Vaccination can expose the immune system to antigen and stimulate the person’s own adaptive response, including relevant memory cells. Receiving antibodies supplies an effector molecule directly and can provide temporary protection. That transfer alone does not generate the same antigen-specific memory response.

Do not claim that a vaccine always prevents infection or that passive immunity lasts indefinitely.

• Vaccination can stimulate the person’s own antigen-specific response and memory.
• Transferred antibodies supply an effector directly.
• Antibody transfer alone is distinguished from generating lasting cellular memory.