Key Terms
Cross-reactivity
Antibody raised against one antigen binds a chemically similar but different antigen. Occurs most often when antibody-an
Affinity
Binding strength between one antibody binding site and one epitope. Avidity: TOTAL strength of all interactions in an an
Adjuvant
Chemical mixed with antigen before injection; causes generalized immune activation; increases antibody production.
Uses
Neonatal jaundice (maternal antibodies bound fetal RBCs; complement activated; hemolysis; bilirubin released = jaundice)
False positive
Test says antigen is present when it is NOT. Cause: cross-reactivity with similar epitopes from other pathogens.
Test sensitivity
Probability of a POSITIVE result when patient IS infected. High sensitivity = low false-negative rate.
Solution
Ligate mouse variable region genes to human constant region genes = chimeric (humanized) mAb. Mostly human; only antigen
Clinical use
CD4 T cell monitoring in HIV patients.
Plantibodies
Antibody genes cloned into plants; potentially cheaper production. ZMapp (Ebola) used tobacco plants; three mAbs combine
Precipitin
Visible antigen-antibody lattice complex that settles out of solution. Lattice forms when antibodies (two binding arms e
Polyclonal antisera preferred for precipitin tests
Multiple epitope binding makes lattice formation more likely. mAbs bind single epitope; lattice forms poorly.
Zone of antibody excess
Not enough antigen; no visible precipitin. Zone of equivalence: optimal ratio; maximum precipitation.
Purpose
Count and quantify specific cell subsets in a mixed population. Method:
Advantage over precipitin ring test
Requires less serum; no mixing risk; arc is stable.
Flocculant
Like a precipitin but involves INSOLUBLE antigens (lipids); lipids cannot precipitate; foaming observed instead.