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




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




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



- Commonest

- Function is Complement fixation

- cross Placenta



- Function is localised protection secretions



- function is complement fixation

- immature Ig

- largest of the five

- can't cross placenta



- function is antigen recognition by B cells



- 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