Q.How does immune system work?

Step 1. The first layer of defence is innate immunity — anatomical, physiological, phagocytic and inflammatory barriers that act immediately and non-specifically against any invading pathogen.

Step 2. If a pathogen breaches these barriers, its antigens are captured and displayed by antigen-presenting cells (including dendritic cells) in the lymphoid organs.

Step 3. This triggers acquired immunity: B lymphocytes, once activated by binding antigen and receiving help from T-helper cells, differentiate into plasma cells that secrete pathogen-specific antibodies (humoral immunity), while T lymphocytes, particularly killer T cells, directly destroy infected or abnormal cells (cell-mediated immunity).

Step 4. Antigen-antibody interactions (precipitation, agglutination, opsonisation, neutralisation) and phagocytosis then physically dispose of the pathogen. …

Walk through the innate-then-acquired sequence of events from pathogen entry to …

• Describing only innate or only acquired immunity instead of how the two layers work together …