HLA Antigens and Antibodies/ Complement

MHC region

Responsible for regulation of immune response and graft rejections

Distinguish between self and non-self

Chrom 6

Highly pleomorphic

Class I

Polymorphic heavy chain and Beta 2 microglobulin

Loci A, B, C on NUCLEATED CELLS

Present antigen to CD8 cells

Eliminate tumor, viral, parasites

Antigen to CD8 cytotoxic cells

Class II

Two polymorphic chains alpha-beta

Loci are DR, DP. DQ

Present antigen to CD4 cells

Eliminate of exogenous antigens processed by APCs

Class III

Non HLA genes on the MHC that encode other molecules involved in immune response

Soluble proteins not involved with tissue transplant or antigen presentation to T cells

C2, C4, Factor B (Complement)

Nomenclature

Splits by gene variations

Class 1: HLA-A, HLA-B, HLA-C, HLA-D = Nucleated cells and platelets

Class II: HLA-D (-DR, -DQ, -DP) = B-cells, macrophages, monocytes, endothelial

Class III: Non HLA genes

Inheritance two alleles expressed codominantly

Inherited in blocks

25% will have identical / share no HLA haplotypes

50% will share one HLA haplotype

Public antigens

Binding to epitopes shared by more than one HLA gene product

Only two: Bw4 and Bw6 = All B antigens

Private antigen

One epitope unique for one HLA gene

Ex: B8 or A23

Linkage disequilibrium

Same combos are more common in certain populations

Ex: A2 and A3 common in caucasians

CREGS

Cross reactive groups - share certain structural elements

Antigens that conflict with each other

Microlymphocytotocity test

Test for Class I (antigen ABC)

+ve stain = cell death holes from complement means i has antigen

Microlymphocytotocity procedure

Separation of Lymphs (buffy coat)

Purification of lymphs (centrifuge)

1 ul of cells added to antisera (pt antibody)

5 ul rabbit complement added to plate

Eosin or trypan blue to stain cells

Formalin to stop reaction

Panel reactive antibodies PRA

Potential transplant recipients are screened monthly to monitor for anti-HLA antibodies

Affinity

Initial force of attraction that exists between one epitope combining with ONE antibody

Avidity

Strength of multivalent antibodies to combine with multivalent antigens; the accumulative binding strength of antigen-antibody complexes

IgM = binds to multiple antibodies

Immune complexes

antigen-antibody complexes

Build up: Acute glomerulonephritis, S pyogenes

False positive

cross reactivity and/or interfering substances

Sensitivity

Smallest amount that can be measured in a test, true positives vs false negatives

Specificity

Antibody’s ability to differentiate between two antigens; true negatives vs false positives

Heterophile

antibody detected against a protein in one species reacts with a protein of another species

Prozone

excess antibodies

Postzone

excess antigens

Equilibrium

reaction occurs and is visible

Antigen = Antibody lattice

Factors affecting antigen-antibody relationships

Temp

Exothermic

Endothermic

Salt concentration

Increase avidity by shaking or mixing

Primary response

3-4 days produce IgM

Ends within a few week

Poor specificity

Leaves memory

Secondary response

More rapid increase of IgG

Plateau longer

Slower decrease

Mostly IgG

Stronger/faster/Anamestic (Memory)

Complement general

Heat labile

Acts in cascade effects

Synthesized in liver and macrophages

Attack/Recruit support/ Destroy antigen

Anaphylatoxins

promote vascular and cellular events in acute inflammation

(C3a, C4a, C5a)

Chemotaxins

attracts PMNs and macros (C5a)

Kinin activity

C2b - pain, vascular permeability

Classic pathway

Activated by IgG1, IgG2, IgG3, and IgM

Recognition phase - C1 antibody recognize antigen COMPLEX

Activation phase - C2, C3, C4

Formation phase - C5, C6, C7, C9

C3 convertase —> C5 convertase 

Common pathway

Alternate pathway

Activated by bacterial polysaccharide, aggregates of IgG4, IgA, IgE , and CRP

Chemotaxins —> Anaphylatoxins

C3 converted to C3b

Factor B, D, properidin

—> common pathway

Factor I

inhibits spontaneous activation of complement

STOPS alternate

Factor H

outcompetes Factor B

STOPS alternate

Vitronectin

Binds C5b67 to prevent MAC in host cell

Stops complement

Protectin

Prevents C9 from binding in MAC in host cell

Stops complement

C1 inhibitor

Binds active C1r: C1s, prevents it from cleaving C2 and C4

Stops classical

C4 binding protein

Binds to C4b in C3 convertase

Stops common pathway = no C3 convertase

DAF

competes with factor B for C3b binding

PNH is often deficiency = Stops alternate

CH50 complement measurement

unit is the dilution of complement it takes to lyse 50% of standard RBC solution (hemolysins added)

50% = normal amount of complement

Monitor progress of disease/ classical and common pathway

CH50 autoimmune

Decreased lysis <50% = decreased complement

CH50 Acute phase reaction

Increased lysis >50% = increased complement

Decrease in complement CH50

Utilization associated with circulating immune complexes

Congenital defects

Liver disease —> MASP

Nutritional imbalance

RA, SLE

C1-4 decrease

increased infections

Decrease in all pathwaysC

C3 decrease

After strep glomerulonephritis, SLE, liver disease

Congenital complement issues

Have pyogenic, G-ve infections

Have decreases in phagocytosis

C4 decrease

decreases along with positive anti-DNA and ANA, is diagnostic for SLE

C5-9 decrease

increased bacterial infection, especially Neisseria

C2 decrease

Most common genetic disorder

Common in autoimmune diseases