Download Immunology Basics 1 - 8 Oct 2015

Immunology Basics: I
Objectives: Understand
What is an immune response ?
Jargon; humoral and cellular immune responses
Structure and differential specificity of immunoglobulins
B lymphocyte life cycle and function
Blood transfusion compatibility as a classic example of antibodymediated immune response
Indirect and direct Coombs tests
Neonatal rhesus disease as a classic antibody-mediated disorder
Jargon:
Antibody: a globulin that binds more or less specifically to a
small number of antigens
Antigen: a substance capable of being bound by an antibody,
e.g., viral capsid, bacterial cell wall component, specific proteins,
etc.
Immune response: a biologically observable effect following the
interaction of an antigen with antibodies or lymphocytes;
usually it is inflammation of some sort
Plasma cells: B lymphocytes
IMMUNE RESPONSES
‘Afferent’ pathway
Antigen challenge
presents
Initial detection
by B or T
lymphocytes
Small, sometimes
undetectable
immune response
Amplification of
T or B lymphocyte
population
Large, detectable immune
response
Traditionally…
Immune responses have been termed ‘humoral’ when
involving B lymphocytes and antibodies
Or
‘Cellular’ when involving T lymphocytes, various cytokines
and killer T lymphocytes
IN FACT - these are not as clearcut and there are many
examples of both these ‘systems’ co-operating
AIM: Eliminate the abnormal by digesting them
Immune responses, one way or other, mark abnormal cells and facilitate
digestion
Immunoblogulins: classes
G: Lightest class, commonest type of B cell
A: Found on mucosal linings, especially the gut
( 3 – 5 g / day, more than all others combined, dimers, acid-resistant)
M: Pentamers of class G (e.g. most blood group antibodies)
E(osinophil): Associated with mast cells and histamine
release
D: Always found with IgG on lymphocyte surfaces,
function unclear (absent in birds, recently detected on basophil membranes)
IgG Monoclonal m.w.=150,000Da
Aspirin
m.w.180
Adapted from US FDA at:
http://www.fda.gov/downloads/drugs/developmentapprovalprocess/howdrugsaredevelopedandapproved/approvalapplications/therapeut
icbiologicapplications/biosimilars/ucm292463.pdf, accessed 22 Sep 2013
IgG
‘Crystalline fragment’
(Fc); similar in all
clones
Disulfide
bridges
‘Antibody fragment’
(Fab); SPECIFIC to
clone.
Cartoon of IgM
B lymphocyte responses
- Germ cells live in lymph nodes, Peyer’s patches, spleen, etc
- By a complicated bit of genetics, these cells have INNATE
ability to recognise antigens
- Some circulate and find antigens, others are presented with
antigens by ‘antigen presenting lymphocytes’ (AFFERENT)
- B lymphocyte responds by:
- Secreting a relevant immunoglobulin
- massive reproduction (cloning)
- cloned cells depart lymphnode for circulation
(EFFERENT)
Peyer’s
patches
Courtesy: Boston University School of Medicine
Lymph node
DRAINAGE
Blood transfusion:
a classic antibody-antigen reaction
1900: Landsteiner developed the A,B, AB, O
group system
1940: Lansteiner and Weiner identify the first
Rhesus epitope
Transfusion: adverse reactions
1.
Infection
2.
Volume overload
3.
Fever
4. CLOTTING THEN
5. Haemolysis (DIC)
6.
Allergy to excipients
7. Late-onset immune responses
8. Purpura (mismatched platelets)
PMNs
secreting
complement
9. Transfusion associated lung injury (? HLA
mismatch)
About 10 μm
ABO Compatibility: 1
PLASMA (Only antibodies, negligible antigen)
DONOR
O (anti-A, antiB)
RECIPIENT
O
A
B
AB
OK
A (anti-B)
OK
B (anti-A)
OK
OK
AB (no abs)
OK
OK
OK
OK
OK
RECIPIENT
ABO and Rhesus Compatibility: 2
Packed red blood cells
DONOR
O (anti-A, antiB)
A (anti-B) B (anti-A)
Rh- Rh+
Rh- Rh+ Rh- Rh+
O+
O-
OK
OK
OK
A+
A-
OK
OK
OK
B+
B-
OK
OK
OK
AB+
AB-
OK
OK
OK
OK
OK
OK
OK
OK
OK
AB (no abs)
Rh- Rh+
OK
OK
OK
OK
OK
OK
OK
OK
Blood Groups
Rhesus: Five epitopes, Dd, Cc, Ee Aa Bb
Numerous alleles; ? A membrane transporter;
Short arm Chromosome 1
Rarely allegenic
Europe: Roughly 85% D+ (DD or Dd)
Asia: dd rarer than Europe
The rhesus macaque Macaqua mulatta
Declining importance in clinical immunogenicity
Blood groups
Duffy +/Lewis Le(0) Le(b)
Kell (haemolytic disease of newborn)
MNS
Another 24 systems
Mostly
Glycoproteins
Fucosylproteins
Or
Lipoproteins
Mostly named
after index
family
Coombs test: Direct
Are there antibodies on red cells (autoimmune haemolysis) ?
Anti-coagulated
blood sample
Spin and wash
RBC sample
Challenge with
generic anti-Fc
human globulin
antibody
AGGLUTINATION =
PRESENCE OF Abs
In original sample
Coombs test, Indirect (Blood grouping)
Are there already soluble antibodies in the plasma that will bind to
a proposed red cell transfusion ?
Coagulated
blood sample
Spin for
serum
Add serum to
panel of grouped
red cells
AGGLUTINATION =
PRESENCE OF Abs
In original PLASMA
sample
Add anti-human
globulin
Cross-matching
Rhesus incompatibility mother / foetus:
Classic example of early versus amplified immune response
Para 1
MOTHER: RHESUS NEGATIVE FOETUS: RHESUS POSITIVE = NORMAL OUTCOME
NO afferent: No Foetal / maternal red cell exchange until delivery
- insignificant direct challenge to the Rh+ neonate (small volume) = no direct harm
- immunization of mother at delivery; about 7 days to full-size clones
Para 2
MOTHER: RHESUS NEGATIVE FOETUS: RHESUS POSITIVE
Maternal IgM crosses the placenta
= PREGNANCY LOSS
What is the treatment ? Where does it come from ?
SUMMARY
Jargon
Antibody structure
B lymphocyte function
Blood transfusion as an example
NEXT TIME
Radioimmunoassays
Auto-immune disease
‘Cellular Immunity’
Immune modulating drugs