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Non-specific responses to infection

Microbiology, Immunity and Forensics · The immune response · note 1 of 5

Spec 6.8
A Level only (what this means)A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels mean
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Non-specific responses to infectionSpec 6.8

In short

Non-specific responses act against any pathogen in the same way. Inflammation increases blood flow and brings phagocytes to damaged tissue, lysozyme digests bacterial cell walls, interferon stops viruses replicating in neighbouring cells, and phagocytosis engulfs and digests pathogens in phagocytes.

Inflammation

When tissue is damaged or infected, mast cells and damaged cells release histamine and other signalling molecules (cytokines).

  1. Histamine causes vasodilation of arterioles, increasing blood flow to the area, so the tissue becomes red and warm.
  2. Capillary walls become more permeable, so more fluid leaves the blood as tissue fluid, causing swelling, which may press on nerve endings and cause pain.
  3. Chemical signals attract phagocytes (neutrophils and monocytes that become macrophages), which leave the capillaries and engulf pathogens.

Lysozyme

Lysozyme is an enzyme found in tears, saliva, mucus and in phagocytes. It hydrolyses the peptidoglycan in the cell walls of bacteria. The weakened wall can no longer resist osmotic pressure, so water enters by osmosis and the bacterium bursts (lysis). Lysozyme does not act on viruses.

Interferon

Interferons are cytokines (signalling proteins) released by cells infected with a virus. They diffuse to neighbouring uninfected cells and bind to receptors on the cell-surface membrane. This switches on genes that make enzymes that break down viral mRNA and inhibit protein synthesis. Viral proteins cannot be made, so the virus cannot replicate in these cells and its spread is slowed.

Phagocytosis

  1. A phagocyte (neutrophil or macrophage) recognises a pathogen, often because it is coated with antibodies or has foreign surface molecules, and the pathogen binds to receptors on the phagocyte.
  2. The phagocyte engulfs the pathogen by endocytosis, enclosing it in a vesicle called a phagosome.
  3. Lysosomes fuse with the phagosome and release lysozyme and other hydrolytic enzymes, which digest the pathogen.
  4. Soluble products are absorbed into the cytoplasm. A macrophage then displays pieces of the pathogen's antigens on its surface (antigen presentation) to start the specific response.
Exam tip:

'Non-specific' means the response is the same whatever the pathogen. Do not say it is 'not immune': it is the first part of the innate immune response.

Four stages of phagocytosis: a bacterium binds to receptors on a phagocyte, is engulfed into a phagosome, lysosomes fuse to form a phagolysosome where hydrolytic enzymes digest it, and antigen fragments are displayed on the cell surface. (opens full size in a new tab)
Phagocytosis and antigen presentation by a phagocyte.

Written and checked against the Edexcel International A Level Biology (YBI11) specification · Updated October 2026

Frequently asked questions

What is the difference between innate and adaptive immunity?

Innate (non-specific) responses such as inflammation, lysozyme, interferon and phagocytosis act against any pathogen, quickly and in the same way. The adaptive (specific) response uses B and T cells whose receptors are complementary to one antigen, takes days at first, and produces memory cells for faster future responses.

How do antibodies work?

Antibodies are Y-shaped proteins made by plasma cells. The variable region on each arm has a shape complementary to one antigen. They bind to pathogens and toxins, clump pathogens together (agglutination), make them easier for phagocytes to engulf, and block attachment to host cells.

What do T helper cells and T killer cells do?

T helper cells are activated by antigen-presenting cells and release cytokines that stimulate B cells and T killer cells. T killer cells destroy body cells that display the antigen, such as virus-infected cells, by releasing perforin and enzymes. Both types also form T memory cells.

All 5 questions on The immune response