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#antibodies

20 public questions tagged with this topic.

Immunological Applications

Abzymes are antibodies that:

Catalytic antibodies termed abzymes represent attempt to harness immune binding energy for chemical transformation similar to enzymes that accelerate reactions 10^10 fold by stabilizing transition state through complementarity. Natural enzymes use preorganized active site residues histidine, aspartate, serine triad precisely positioned via folding to provide general acid-base, nucleophile, oxyanion hole stabilization. Abzymes generated by immunization with stable transition-state analogue designed to mimic high energy tetrahedral intermediate of ester hydrolysis such as phosphonate monoester where P-O bond length resembles C-O tetrahedral geometry but non-hydrolyzable. Immune system selects B clones whose paratope complementary to analogue, somatically hypermutated variable regions can position Asp, His, Ser analogous to serine protease active site capable of promoting water activation and nucleophilic attack. Measured kcat enhancements 10^2 to 10^4 over background far below natural enzymes but proof of principle achieved for ester, amide, carbonate cleavage, Diels-Alder pericyclic, and beta-lactam hydrolysis that could degrade antibiotic resistance agents. Recombinant strategies introduce catalytic residues via site-directed mutagenesis, metal binding motifs for zinc dependent hydrolysis, or cofactor flavin to improve turnover. Abzymes remain conceptual prototype illustrating how binding energy can be converted into catalytic activation and potential for designer biocatalysts tailored to therapeutic prodrug activation.

Ref: Lerner et al Science 1991 252:659 catalytic antibodies abzyme; Shabat et al Transition state analog phosphonate ester.

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Immunological Applications

Monoclonal antibodies are produced by:

Mammalian antibody-secreting plasma cells are terminally differentiated, possessing an extensively expanded endoplasmic reticulum and unfolded protein response activated to sustain immunoglobulin production at up to 10,000 molecules per second, but these cells quickly trigger p53 dependent apoptosis and survive only days in vitro. To overcome limited lifespan, Georges Kohler and Cesar Milstein in 1975 created hybridoma technology that couples specificity donor with immortal partner. Splenic B lymphocytes isolated from hyperimmunized mouse provide functional heavy and light chain loci after somatic hypermutation and class switch recombination for high affinity binding. Murine myeloma lines like SP2/0-Ag14, NS0, and X63-Ag8.653 lack antibody secretion due to loss-of-function immunoglobulin genes but express constitutive telomerase, dysregulated N-Myc, loss of p16INK4a, autocrine IGF-1 signaling, and robust glycolytic metabolism supporting unlimited division in conventional media. Fusion using polyethylene glycol generates heterokaryons whose nuclei fuse, chromosome segregation yields stable hybrids secreting single idiotype. Cloning by limiting dilution at 0.3 cells per well ensures monoclonality, enabling establishment of master cell banks, GMP production, and consistent bioreactor harvests without repeated animal immunization.

Ref: Kohler & Milstein Nature 1975 256:495 hybridoma; Alberts Molecular Biology of Cell 6th ed Chapter 8 monoclonal production.

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Immunological Applications

Polyclonal antibodies differ from monoclonal antibodies because they:

Immunization with a complex protein or whole pathogen simultaneously displays many surface features that can be recognized by the adaptive immune system. Each epitope activates distinct naive B cells bearing complementary B cell receptors generated through VDJ recombination and junctional diversity, driving clonal expansion in germinal centers with help from follicular helper T cells. Differentiation produces plasma cells secreting antibodies with different paratopes, isotypes, and affinities that collectively coat the same antigen particle. The resulting serum therefore constitutes a heterogeneous mixture capable of binding multiple determinants at once, providing high avidity through simultaneous attachment, lattice formation, precipitation, and efficient complement fixation via classical pathway. This breadth enhances pathogen neutralization and improves diagnostic sensitivity because even if one epitope mutates, others remain recognized. However heterogeneity causes lot-to-lot variation and broader cross-reactivity against conserved motifs. In contrast, monoclonal population originating from single fused cell carries identical variable domains fitting only one epitope shape with uniform binding kinetics, illustrating fundamental difference between polyclonal multi-epitope recognition and single specificity.

Ref: Kuby Immunology 8th ed Chapter 4 Antibody binding; Janeway Immunobiology NCBI Bookshelf NBK27130 polyclonal multi-epitope recognition.

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Immunological Applications

Which of the following is an example of therapeutic monoclonal antibody?

Cetuximab chimeric IgG1 mAb 152 kDa murine variable regions grafted human constant domains preserving antigen binding specificity reducing HAMA response versus purely murine. Target EGFR HER1 encoded EGFR 7p11.2 overexpressed colorectal lung HNSCC via amplification autocrine loop. Physiologic ligands EGF TGF-alpha amphiregulin bind ECD III inducing conformational change exposing dimerization arm domain II allowing homo hetero-dimerization HER2 HER3 autophosphorylation tyrosines Tyr1068 Tyr1086 Tyr1173 recruiting adaptors Grb2 Shc activating KRAS GTP exchange GDP GTP triggering BRAF MEK ERK proliferation Elk1 PI3K p110alpha generating PIP3 Akt mTOR survival. Cetuximab competitively occupies ligand-binding site affinity 0.1 nM exceeding EGF 1 nM blocks ligand access inhibits dimer formation promotes internalization degradation clathrin pits reducing nuclear translocation where EGFR acts transcription cofactor cyclin D1 iNOS. Fab also mediates ADCC via NK Fc gamma RIIIa. Efficacy confined RAS wild-type because constitutive KRAS G12D G13D NRAS mutations bypass receptor requirement rendering blockade ineffective necessitating companion diagnostic KRAS testing before use explaining infusion reaction due preexisting IgE alpha-gal epitope murine Fab glycosylation mammalian expression system.

Ref: FDA Erbitux Cetuximab EGFR MOA Label; NEJM Cetuximab Colorectal KRAS Wild-type 2008 Van Cutsem; Janeway EGFR Antibody Therapy ADCC Mechanism.

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Immunological Applications

Monoclonal antibodies are produced by:

Monoclonal antibodies originate immortalized hybridoma lines fusing single antibody-secreting B lymphocyte with myeloma partner preserving exactly one immunoglobulin gene rearrangement producing uniform paratope. Protocol begins immunization BALB/c mice purified antigen HER2 extracellular domain mixed Freund's adjuvant stimulating germinal center spleen. Four days after final booster splenocytes enriched plasma blasts expressing high-affinity surface IgG harvested. Fusion mediated PEG 1500 or electrofusion aligning cells pearl chains creates heterokaryons containing nuclei both parents tetraploid genome combining proliferative machinery myeloma P3X63Ag8U deficient HPRT and functional Ig heavy light chain variable regions B cell. Screening supernatants 10 days HAT medium ELISA identifies wells secreting antibody binding desired epitope single specificity affinity parent clone e.g., 10 nM. Cloning limiting dilution ensures monoclonality 0.5 cell per well. Resulting hybridoma inherits indefinite division activated c-myc autocrine IL-6 robust ER chaperone capacity folding continuous Ig secretion under Ig enhancers. Bioreactor expansion yields liters supernatant purified Protein A affinity chromatography producing uniform reagent defined sequence enabling therapeutics trastuzumab rituximab derived hybridoma technology now adapted recombinant CHO expression systems large-scale manufacturing.

Ref: Kohler and Milstein Nature 1975 Hybridoma Monoclonal Generation; Janeway Hybridoma Technology Production Chapter 5; Lodish Antibody Production Hybridoma Cells Method.

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Immunological Applications

Polyclonal antibodies differ from monoclonal antibodies because they:

Polyclonal antibody preparations heterogeneous mixture immunoglobulin molecules diverse B lymphocyte clones responding complex immunogen multiple antigenic determinants repetitive epitopes. Each naive B cell generates unique BCR random recombination RAG-mediated VDJ joining heavy chain variable diversity joining segments VJ joining light chain kappa lambda diversified junctional addition non-templated nucleotides TdT and somatic hypermutation germinal centers introducing point mutations rate 10^-3 per base division selecting higher affinity via follicular dendritic cell presentation. Immunization whole bacteria S. aureus viral glycoprotein influenza hemagglutinin toxoid tetanus toxoid containing repetitive carbohydrates conformational proteins activates numerous clones secreting IgG subclasses IgG1 IgG2 affinities 10^-6 to 10^-11 molar avidities multivalency. Serum contains antibodies recognizing linear peptide epitopes 8-12 residues discontinuous conformational surfaces formed distant residues folded together carbohydrate moieties neoepitopes formaldehyde treatment. Polyepitopic recognition enhances lattice formation C1q classical complement activation improving pathogen agglutination opsonization phagocytosis although batch variability cross-reactivity homologous antigens limited reproducibility complicate standardization compared monoclonal reagents uniform specificity.

Ref: Janeway Immunobiology 9th ed Polyclonal vs Monoclonal Diversity Chap 5; NCBI Bookshelf Antibody Diversity Mechanism; Campbell Immunology Antibody Response Polyepitopic.

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