hypersensitivity and autoimmunity

Question 1

mechanism of type I hypersensitivity (allergy)

Answer 1

principally arises from the inappropriate synthesis of IgE in response to allergen exposure. This causes the release of inflammatory mediators such as histamine and prostaglandins from mast cells.

Question 2

effects of type I hypersensitivity

Answer 2

-mucosal oedema
-capillary leakage
-secretions
-smooth muscle -contraction
vasodilation

Question 3

Mechanism of type II hypersensitivity

Answer 3

IgM and IgG antibodies are released against antigens on the surface of cells, these can be exogenous or self.

Question 4

effects of type II hypersensitivity

Answer 4

causes tissue damage by:

• complement activation
• Fc (surface) binding of Ig and stimulation of phagocytes
• antibody dependent cytotoxicity
• stimulation or inhibition on target cell function

Question 5

mechanism of type III hypersensitivity

Answer 5

caused by antibodies forming complexes. This is a normal process but can cause problems when they are deposited in places they shouldn’t be.

Question 6

effects of type III hypersensitivity

Answer 6

deposition of antibody complexes are deposited locally in one tissue or throughout the body in many tissues.

Question 7

mechanism of type IV hypersensitivity

Answer 7

not caused by antibodies but by Th1 cells. An exogenous antigen with alow molecular weight binds with an endogenous protein carrier, Th1 cells rcognise the antigen and release cytokines producing an inflammatory response. The Th1 cells acn also be activated by microorganisms such as mycobacteria.

Question 8

Th1 cell function

Answer 8

stimulate the activation of macrophages and cell-mediated immunity.

Question 9

Th2 cell function

Answer 9

stimulate the activation of B lymphocytes

Question 10

Atopy

Answer 10

a state of sub-clinical immune sensitisation, associated with type 1 hypersensitivity.

Question 11

tolerance

Answer 11

The process whereby the immune system avoids producing damaging reactions against self antigens.

Question 12

central tolerance mechanism

Answer 12

autoreactive T&B cells are deleted during cell maturation

Question 13

peripheral tolerance mechanism

Answer 13

autoreactive cells that escape the immune system are inhibited

Question 14

what causes autoimmunity?

Answer 14

a breakdown in any of the tolerance mechanisms

Question 15

aetiology of autoimmunity

Answer 15

• genetic factors (inheritance of particular HLA (MHC) types)
• immune regulatory factors (defective tolerance induction, defective peripheral tolerance mechanisms)
• hormone factors ( particularly female hormones)
• environmental factors (infectious agents, sunlight, drugs, chemicals, nutritional factors)
• ‘other’ factors (trauma or malignant disease)

Question 16

pathogenic mechanisms of autoimmune diseases

Answer 16

same as in normal immune responses.
so:
- cellular (T cell) or humoral (Bcell) activity
-autoantibody activation of complement-mediated inflammation.
-immune complex formation
-recruitment of innate immune components such as phagocytes/ cytokines/ NK cells etc.

Question 17

HLA genes

Answer 17

genes that code for the MHC, if translation of these genes goes wrong along with environmental factors this can cause autoimmunity.

Question 18

spectrum of clinical autoimmune disorders

Answer 18

spectrum from asymptomatic to chronic life-threatening disorders.

Question 19

organ specific autoimmune disorders

Answer 19

immune system attacks one organ, eg autoimmune endocrine disorders

Question 20

non-organ specific autoimmune disorders

Answer 20

immune system attacks more than one organ or non-organ tissues, eg. joints

Question 21

where is the site of central tolerance for B and T cells?

Answer 21

T cells- thymus

B cells - bone marrow