MOD2 Antigen Antibody Reactions

naturally occurring antibodies

abs that can develop without exposure to foreign red cell antigens

occur without hx of transfusion or pregnancy

immune antibodies

produced in response to exposure to foreign red cell antigen

can occur during transfusion or pregnancy

alloantibody

ab developed against foreign red blood cell antigen

autoantibody

ab developed against self-antigens

outcomes of antigen-antibody reactions in vivo (pt)

increased opsonization of ab coated red cells

complement activation

activation of proinflammatory responses due to hemolysis

increased opsonization of ab coated red cells

outcome of ag-ab rxn in pts

red cells coated w abs are tagged for recognition

cells bind to Fc receptors on macrophages → extravascular hemolysis

complement activation

outcome of ag-ab rxn in pts

results in

• release of anaphylatoxins

• intravascular hemolysis

• extravascular hemolysis

activation of proinflammatory responses due to hemolysis

outcome of ag-ab rxn in pts

release of free hemoglobin into circulation → accumulation of unbound hgb → proinflammatory effects → contribute to systemic infl response

agglutination

1. sensitization → binding of abs to ags on red cell surface → not visible

2. antigen-antibody lattice formation → complexes link to form lattice → visible clumping

hemolysis

can be caused by red cell ag-ab rxns if complement is activated → cell lysis

rarely seen in vitro → use EDTA specimens — binds Ca2+ needed for complement pathway

neutralization

occurs when ab’s activity is blocked by corresponding ag in soluble form

used to neutralize specific ab in pt plasma → easier to detect other abs that may be present

ex. lewis abs, anti-P1, anti-chido, anti-rodgers, anti-Sda

solid phase adherence

known red cells fixed to solid-phase well + pt plasma

if plasma has corresponding abs → cells bind to ags

add indicator → visual confirmation — pos: fixed to well, neg: button

gel technology

microtubes filled w gel matrix containing AHG

pt plasma + reagent indicator → ag-ab complex forms → binds to AHG → suspended in gel column

molecular detection

pt dna extracted and amplified → specific sequences detected using labeled probes

hydrogen bonds

attraction of electronegative atoms for hydrogen of nearby molecule

carbohydrate antigens → ABH, li, P1, M, N

exothermic rxn

IgM antibodies

van der waals forces

weak attractive force between electron cloud + exposed nucleus of molecules

protein antigens → Rh, Kell, Duffy, Kidd

endothermic rxn

electrostatic/ionic bonds

electrostatic attraction of pos/neg charges on ags/abs

influenced by pH, ionic strength, dielectric constant of rxn

carbohydrate and glycoprotein antigens → ABH, li, P1, Lewis, M, N

exothermic rxn

hydrophobic interactions

two hydrophobic surfaces drawn together → dec total surface area + dec exposure to H2O

protein antigens → Rh, Kell, Duffy, Kidd

endothermic rxn

IgG antibodies

physical characteristics of ags affecting agglutination

number of antigen sites → more sites per RBC = greater likelihood ab finds + binds to 2 adjacent RBCS

projection of antigen from membrane → allow ab to span the gap btwn cells

antibody size affecting agglutination

distance between RBCs in saline → 25nm

IgG abs span 14nm → cannot bridge two cells on its own

IgM abs span 35nm → can aggl cells on their own

chemically modified IgG → can aggl cells

in vitro conditions affecting agglutination

• pH → complexes form best at 6.5-7.5

• temp → IgM best at/below 22, IgG best at 37

• centrifugation → bring cells closer tgh

• time → too short: weak rxn, too long: complexes disassociate

• enhancement media → low ionic strength soln LISS, polyethylene glycol PEG, albumin, enzymes, anti-human globulin AHG

non saline reactive/incomplete antibodies

do not produce agglutination → only sensitization occurs

usually IgG, reacts best at 37deg

detected using AHG technique or enhancement techniques

saline reactive antibodies

produce visible agglutination

complete antibodies → usually IgM

reacts usually 4-22deg, some 37deg

ex. anti-A, anti-B

exception: antihuman globulin AHG

antihuman globulin AHG

IgG antibody but saline reactive

targets other IgG abs → detects RBCs that have been sensitized by incomplete abs → bridges gap between RBCs → visible agglutination