Definition
Immune system produces antibodies against antigens
Immune system remembers
- second exposure to antigen generates greater & more rapid response
Two types of immunity
- humoral
- cell mediated
Two types immunization
- active
- passive
Development
Lymphocyte precursors come from bone marrow
- migrate to modifying organ
- then return to nodes & bone marrow
T Cells
Lymphocytes that populate thymus
Mediate cellular immunity
Differentiate into 4 types
1. Helper / Inducer T Cells (CD4)
2. Suppressor T Cells (CD8)
3. Killer T Cells (CD8)
4. Memory T Cells
Helper T Cells
- involved with regulation of antibody production by B cells
Killer cells
- destroy foreign cells
B Cells
Cells that populate spleen & liver
Mediate Humeral Immunity
B lymphocytes differentiate into
- pasma cells
- memory B cells
Humoral Immunity
Basic Process
Foreign proteins that enter body called antigens
- ingested by macrophages
- macrophages expose part of ingested antigen plus Major Histocompatibility Complex (MHC) on surfaces
Macrophages then contact lymphocytes
- CD4 (TH) cells bind to Antigen + MHC II on surface of macrophage
- CD4 cells become activated & contact B cells
- B cells activated
- proliferate
- transform into Memory B cells & plasma cells which secrete antibodies
Immunoglobulins
5 types
- shaped like Y
- stem is Fc Fragment
- arms are Fab Fragment
Consist of
1. Two light chains
- two types
- Kappa & Lambda
2. Two heavy chains
IgG
- Commonest
- Function is Complement fixation
- cross Placenta
IgA
- Function is localised protection secretions
IgM
- function is complement fixation
- immature Ig
- largest of the five
- can't cross placenta
IgD
- function is antigen recognition by B cells
IgE
- function is Reagin activity
- releases Histamine from mast cells
Major Histocompatibility Complex
Located on short arm of Chromosome 6
- code Glycoproteins located on surfaces of all cells
- function in distinguishing self from non self
- three major loci
Class I Loci
- encode for HLA-A, HLA-B, HLA-C
- found on all cells except RBC
- primary factors in Self-recognition & Development of tolerance
Class II Loci
- encode for HLA-DP, HLA-DQ, HLA-DR
- involved in Antigen presentation to Helper T cells
- present on Antigen Presenting Cells
- macrophages, B Cells, activated T cells
Class III Loci
- encode for proteins of complement cascade
Complement System
When antigens combine with circulating Ig
- cells lysed
- bacteria opsonised (phagocytosed)
- WCC attracted to antigen
- histamine released
Mediated by plasma enzymes called complement
- enzymes numbered C1 to C9
- C1 binds to Ig that have bound antigen
- triggers series of events that activates other components of system
- C3 facilitates phagocytosis of micro-organisms
- C5-9 inserted into cell membranes as pores
- C5a & C9a cause Histamine release from mast cells
- C5a is chemotactic for neutrophils
Cellular Immunity
Mediated by CD8 cells
- activated when presented with antigen & MHC-I protein
Proliferate & differentiate into
- Memory T cells
- Cytotoxic T cells
- Suppressor T cells
Cytotoxic cells kill by
1. Insertion of pore-forming protein into target’s cell membranes
2. Insertion of toxins into target cells
Suppressor cells help to terminate immune response
Memory cells responsible for accelerated response to second exposure