Lecture 9- T cells in infection

Question 1

Humoral immunty

Answer 1

The extracellular spaces are protected by the humoral immune response, in which antibodies produced by B cells cause the destruction of extracellular microorganisms and prevent the spread of intracellular infections.

Question 2

Cell-Mediated Immunity

Answer 2

Cells are protected by CM immunity in which products of T cells protect the body from virus/cancer by killing abnormal/virus affected cells.

Question 3

Types of lymphocytes produced by the thymus

Answer 3

Both express T cell receptors for antigen (TCR)
Both have CD3 (linked to TCR and signals cells)
1) Helper T cells: CD4 on surface interact with Class 2 MHC
2) Cytotoxic T cells: CD8 on surface interact with Class 1 MHC
3) Regulator T cells: often identified by the additional CD45RB

Question 4

Types of responses of T cells

Answer 4

Cytotoxic > kill cells
Helper > produce helper cytokines that assist other cells to respond
Regulator > produce inhibitory CKs

Question 5

How can T cells bind to antigens

Answer 5

Can only bind to antigenic epitopes presented to them on the surface of cells by specialised stuctures MHC determinants.

Question 6

MHC genes are? In humans this is?

Answer 6

Major Histocompatibility Complex. In humans this is HLA.

• Present antigens to T lymphocytes
• involved in graft rejection
• Class 1 and 2

Question 7

Similarities and differences of class 1 and 2 HLA genes

Answer 7

BOTH co-dominantly expressed. Both polymorphic genes

Class 1 HLA: Surface structures on virtually all nucleated cells
Present antigenic peptides to CD8 T cells
HLA-A HLA-B HLA-C each code for a single polypeptide.

Class 2 HLA: Surface structures found on specialised APC and B cells
Present antigenic peptides to CD4 T cells
HLA-DP, DQ, DR each code for TWO polypeptides.

Question 8

Two different ways of Antigen Presentation

Answer 8

CLASS 1: antigenic fragments usually from infectious process in the cell. During infection virus material is synthesized, some fragments however appear on the surface of ‘Class 2 MHC’ Structures. These can be recognised by cytotoxic T lymphocytes > cell death

CLASS 2: Antigenic material uptaken (phagocytosed) by APC or B-cells, broken down/degraded into smaller fragments then peptide fragments presented by ‘class 2 MHC structures’, to Helper T lymphocytes

Question 9

Flow diagram of T cell activation

Answer 9

virally infected cells present antigens to cytotoxic precursors > bind strongly, T cells activated > with help of CKs from Helper T cells, they divide and differentiate > effector cells that can recognise and kill target cells.

Question 10

General model of lymphocyte activation

Answer 10

First activation signal) antigen binds to B or T cell surface receptors. The cell then expresses receptors of cytokines (growth hormones)
Second activation signal) appropriate cytokine (usually from helper T cells), lymphocyte now fully activated and can respond.

Question 11

What are cytokines? What is their function, how are they produced

Answer 11

immunological “hormones”
Regulate inflammatory /immune responses
produced by CD4 helper T cells, as well as other cells

Question 12

Why do some people get allergies and others dont

Answer 12

Because some people have an overactive AB response against non-harmful substances

Question 13

Immune-mediated tissue damage

Answer 13

The immune systems reaction can be so strong it can cause tissue damage
eg) hepatocyte damage in hep B response

Question 14

Autoimmunity

Answer 14

produce AB against yourself.

eg) pernicious anaemia: AB against intrinsic factor or parietal cells, can’t absorb B12