Introduction to Immunology Immunity


The Immune Response: The last line of defence



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ANSC 107 Lecture-Lecture 10

The Immune Response: The last line of defence

  • The general idea is this:
  • Something has got through the first lines of defence, and entered the body in force.
  • If the body has been invaded by this particular nasty thing before, then special Lymphocytes called B-Cells and T-Cells are able to recognise these specific pathogens, and overwhelm them (thanks to the `immune system memory’)
  • If this is a new invasion, then the B-Cells will learn how to fight this invader. (and then remember for next time).

Specific Antigen Recognition

  • B-cell or
  • T-cell
  • Surface receptor molecule
  • Nasty thing
  • This lymphocyte
  • recognizes the
  • red pathogen
  • B-cell or
  • T-cell
  • This one doesn’t

Generating Variety

  • The receptor molecule is a protein, encoded by a highly variable
  • gene. There is essentially a combinatorial library of parts in the genome:
  • DNA
  • Each B or T cell makes up its receptor by choosing:
  • one of these
  • and one of these
  • and one of these, etc…
  • The result is that an enormous variety of possible surface receptors
  • could be chosen. This is effectively a method for generating random
  • receptors. Since recognition need not be exact, it is possible in
  • practice for a B or T cell to generate a receptor which matches any
  • given antigen.

Generating variety II

  • In addition, B-Cells (but not so much T cells) also undergo somatic
  • hypermutation. Somatic just means in the body, during one’s lifetime.
  • Hyper just means `a lot’. In a nutshell:
  • 1. Thru, somatic hypermutation a B-cell recognizes an antigen that it has not come in contact with before.
  • 2. Then this leads to this B-cell dividing, creating daughters
  • who produce the same receptor.
  • 3. But these daughter cells may have mutations in their library which will allow some of the daughters may recognise the antigen even better.
  • 4. Back to 1.

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