Immunological Applications

Immunological Applications

Subunit vaccines contain:

Whole pathogen vaccines contain complex mixture of antigens including immunodominant protective components but also many irrelevant proteins plus reactogenic factors such as lipid A endotoxin activating TLR4 causing fever, pertussis toxin ADP-ribosylating Gi, increasing reactogenicity and rare adverse events. Subunit vaccine strategy improves safety by purifying protective antigens through biochemical fractionation, recombinant expression, or synthetic peptide synthesis excluding toxic moieties. Hepatitis B vaccine exemplifies recombinant subunit: hepatitis B small surface antigen HBsAg gene cloned into Saccharomyces cerevisiae yeast downstream of alcohol dehydrogenase promoter, protein expressed self-assembles into 22 nanometer virus-like particles composed of 100 monomers with disulfide crosslinks displaying conformational neutralizing a determinant in second hydrophilic loop, particles lack viral DNA completely noninfectious. Acellular pertussis vaccine includes genetically detoxified pertussis toxin PT9K/129G where arginine 9 to lysine and glutamic acid 129 to glycine mutations abolish ADP-ribosyltransferase activity, filamentous hemagglutinin adhesion factor, and pertactin 69 kDa outer membrane protein, eliminating whole cell lipopolysaccharide linked to high fever and protracted crying observed with whole cell DTP.

Ref: NCERT Class XII Biology subunit purified antigen VLP HBsAg; Pulendran Nat Immunol 2011 alum NLRP3 adjuvant acellular pertussis.

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Immunological Applications

Live attenuated vaccines differ from inactivated vaccines because they:

Live attenuated vaccines developed through classical virology approach reducing pathogenicity while retaining replicative capacity that mimics natural infection without causing severe disease. Attenuation strategies include serial passage in heterologous host cells like chick embryo fibroblasts, embryonated eggs, or at subphysiologic temperature 25 to 33 degrees cold adaptation accumulating adaptive mutations in polymerase genes L and P reducing transcription efficiency in human cells at 37 degrees, plus mutations in surface glycoprotein cleavage sites reducing fusogenicity and in interferon antagonism proteins NS1 and V impairing immune evasion. Resulting strain enters mucosal epithelia via natural route intranasal or oral, expresses entire antigen repertoire including conformational fusion protein prefusion state, matrix and nucleoprotein providing CD8 epitopes conserved across strains that are destroyed by formalin inactivation crosslinking fusion peptide, and replicates limitedly to titers 10^3 to 10^4 increasing antigen dose tenfold from inoculum. This mechanistic insight supports diagnostic and therapeutic applications while reinforcing core immunological and cell biology principles taught in advanced curricula.

Ref: Plotkin Vaccines 7th ed live attenuated replication PAMP; Abbas Cellular Molecular Immunology Sabin polio reversion risk.

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Immunological Applications

DNA vaccines work by:

DNA vaccination concept bypasses conventional protein purification manufacturing by delivering genetic blueprint encoding protective antigen allowing host cells to synthesize immunogen in situ mimicking viral infection while noninfectious. Plasmid vector engineered with strong eukaryotic promoter typically human cytomegalovirus immediate early enhancer promoter driving high transcription, chimeric intron improving mRNA stability and export, Kozak consensus GCCACCATGG for efficient translation initiation, antigen coding sequence codon optimized for human usage bias replacing rare codons to increase expression tenfold, and bovine growth hormone polyadenylation signal specifying cleavage and poly-A adding 200 adenines. After intramuscular injection with needle or gene gun gold particles, myocytes and keratinocytes internalize negatively charged plasmid via macropinocytosis, plasmid enters nucleus through nuclear pore complex during mitosis when nuclear envelope breaks down or via active import mediated by importin. This mechanistic insight supports diagnostic and therapeutic applications while reinforcing core immunological and cell biology principles taught in advanced curricula. This mechanistic detail underpins practical applications in diagnostics, vaccine design, and biopharmaceutical manufacturing.

Ref: Ulmer et al Science 1993 DNA vaccine CMV promoter MHC I II; NIH Vaccine plasmid CpG TLR9 adjuvant mechanism.

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Immunological Applications

Agglutination reactions are based on:

Agglutination reaction visual detection of antigen antibody crosslinking forming large lattices precipitating out of suspension forms basis rapid diagnostics usable at bedside without sophisticated equipment. Mechanism relies on multivalent antigen expressed repetitively on particulate carriers like erythrocytes expressing ABO antigens A trisaccharide with terminal N-acetylgalactosamine, Rh D polypeptide 12 transmembrane helices, bacteria displaying O polysaccharide lipopolysaccharide, or inert latex beads coated with purified recombinant protein, crosslinked by multivalent antibodies. IgM pentamer 900 kDa with ten Fab arms particularly efficient due to span 35 nanometers allowing bridging of multiple cells simultaneously causing clumping visible to naked eye. IgG bivalent can agglutinate but requires enhancement media albumin reducing zeta potential electrostatic repulsion negative charge surrounding erythrocytes, or protease bromelain cleaving sialoglycoproteins reducing surface charge. Reaction kinetics obey Heidelberger-Kendall precipitin curve where antibody excess forms soluble small complexes, equivalence zone yields maximal insoluble aggregates settling, antigen excess resolubilizes. Direct agglutination test mixes patient red cells with commercial antisera anti-A, anti-B providing ABO typing within two minutes.

Ref: Kuby Immunology Heidelberger-Kendall agglutination lattice IgM; CDC blood typing direct indirect agglutination equivalence.

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Immunological Applications

Immunoblotting is also known as:

Immunoblotting approach later termed Western blot combines size based separation with specific antibody detection, becoming gold standard for protein confirmation. Methodology introduced by Harry Towbin and Neal Burnette 1979: sodium dodecyl sulfate anionic detergent disrupts secondary and tertiary structure coating polypeptide backbone with uniform negative charge ratio approximately 1.4 gram SDS per gram protein, allowing electrophoretic mobility in polyacrylamide gel to correlate inversely with logarithm of molecular weight separating proteins from 10 to 300 kDa according to pore size determined by acrylamide percentage and bis-acrylamide crosslinking. Proteins then transferred electrophoretically from gel to nitrocellulose or polyvinylidene difluoride PVDF membrane via wet or semi-dry blotting applying electric field 100 volts for one hour preserving spatial pattern, membrane with high protein binding capacity via hydrophobic interaction. Membrane blocked with nonfat dry milk five percent or bovine serum albumin three percent containing Tween-20 to prevent nonspecific adsorption of antibodies. This mechanistic insight supports diagnostic and therapeutic applications while reinforcing core immunological and cell biology principles taught in advanced curricula.

Ref: Towbin et al PNAS 1979 76:4350 Western blot SDS-PAGE PVDF; NCBI Bookshelf immunoblotting Towbin transfer.

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Immunological Applications

RIA stands for:

Radioimmunoassay developed by Solomon Berson and Rosalyn Yalow 1960 represented first method achieving picogram sensitivity for protein hormone quantification, earning Nobel Prize Physiology 1977. Principle competitive: fixed limiting amount of specific antibody incubated with constant amount of radiolabeled antigen tracer and variable unlabeled sample. Radiolabel typically iodine-125 introduced onto tyrosine residues via chloramine T oxidation producing reactive iodonium ion electrophilically substituting aromatic ring or via lactoperoxidase enzymatic iodination preserving biological activity, specific activity up to 100 microcurie per microgram allowing gamma counting, half-life 60 days. Unlabeled analyte competes for antibody binding sites reducing bound tracer proportionally. Separation of bound versus free fractions achieved by precipitation with secondary anti-immunoglobulin antibody forming insoluble immune complex, or polyethylene glycol 6000 increasing macromolecular crowding causing precipitation, or charcoal adsorption of free antigen. Bound radioactivity measured in gamma counter, Scatchard plot analysis yields affinity constant and concentration via dose-response curve. Sensitivity reaches low picogram per ml for insulin enabling discovery of hormone heterogeneity and antibodies in diabetic sera.

Ref: Berson & Yalow J Clin Invest 1960 39:1157 Radioimmunoassay iodine-125; Lodish Molecular Biology competitive binding tracer.

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Immunological Applications

ELISA is commonly used for:

Enzyme-linked immunosorbent assay revolutionized immunodiagnostics by converting antigen antibody binding into measurable enzymatic colorimetric signal without radioactivity, originally described by Eva Engvall and Peter Perlmann 1971. Polystyrene microtiter plate with high binding capacity via hydrophobic interaction adsorbs capture antibody coated overnight at alkaline pH 9.6 carbonate buffer 1 to 10 microgram per ml. Non-specific sites blocked with protein bovine serum albumin five percent, casein, or nonfat milk to prevent background adsorption through hydrophobic pockets. Sample containing antigen such as viral capsid HIV p24, cytokine IL-6, or hormone insulin incubated allowing specific capture, unbound material removed by repeated washes with phosphate buffered saline containing 0.05 percent Tween-20 disrupting weak interactions. Detection uses secondary antibody conjugated covalently to horseradish peroxidase or alkaline phosphatase via periodate oxidation forming Schiff base. Addition of chromogenic substrate tetramethylbenzidine TMB with hydrogen peroxide yields oxidation to blue diimine measured after sulfuric acid stopping as yellow product absorbance 450 nm proportional to analyte concentration via four-parameter logistic standard curve with dynamic range three logs.

Ref: Engvall & Perlman Immunochemistry 1971 ELISA; Alberts MBoC ELISA HRP TMB sandwich principle diagnostic.

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Immunological Applications

Ado-trastuzumab emtansine is used against:

HER2 positive metastatic breast cancers progressing after trastuzumab plus chemotherapy develop resistance mechanisms including truncated p95HER2 lacking extracellular binding epitope, upregulation of MUC4 masking epitope, activation of downstream PIK3CA H1047R mutation, and alternative receptor tyrosine kinase signaling AXL. Ado-trastuzumab emtansine also called T-DM1 extends HER2 targeting beyond signaling inhibition delivering cytotoxic maytansine chemically. Trastuzumab backbone retains anti-signaling activity via inhibition of HER2 heterodimerization and metalloprotease cleavage, suppression of PI3K-AKT, plus Fc mediated antibody dependent cellular cytotoxicity through FcγRIIIa. Chemical linker SMCC succinimidyl trans-4-(maleimidylmethyl) cyclohexane-1-carboxylate forms stable non-reducible thioether bond between cysteine sulfhydryl of antibody and primary amine of DM1 derivative maytansine that binds tubulin near vinca site with binding affinity 100 times vincristine inhibiting microtubule polymerization, causing aberrant mitosis with multipolar spindles and subsequent mitochondrial apoptosis. After HER2 mediated internalization to lysosome acidic proteases cathepsin B and L degrade antibody polypeptide releasing active metabolite lysine-MCC-DM1 retaining microtubule inhibitory activity while sparing systemic exposure because stable thioether prevents premature release in plasma, mitigating myelosuppression and neuropathy.

Ref: Verma et al NEJM 2012 367:1783 EMILIA T-DM1 HER2 DM1 non-cleavable; FDA ado-trastuzumab emtansine label.

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Immunological Applications

Brentuximab vedotin targets:

CD30 antigen also designated TNFRSF8, 120 kDa type I transmembrane glycoprotein member tumor necrosis factor receptor superfamily characterized by cysteine rich domains extracellularly and TRAF binding motifs intracellularly activating NF-kB, transiently expressed on activated B and T lymphocytes but constitutively highly expressed on Reed-Sternberg giant cells of classical Hodgkin lymphoma and anaplastic large cell lymphoma ALCL, and small subset cutaneous T cell lymphomas, making near tumor specific target with minimal normal tissue expression limited to activated immune cells conferring favorable safety margin. Brentuximab vedotin pioneered antibody-drug conjugate class, comprising chimeric anti-CD30 IgG1 antibody cAC10 variable regions murine grafted onto human constant selected for high internalization rate, conjugated via protease-cleavable valine-citrulline dipeptide plus PABC self-immolative spacer to monomethyl auristatin E synthetic analogue of marine natural product dolastatin 10 derived from sea hare Dolabella auricularia that binds tubulin at vinca domain inhibiting polymerization. This mechanistic insight supports diagnostic and therapeutic applications while reinforcing core immunological and cell biology principles taught in advanced curricula.

Ref: Younes et al NEJM 2010 363:1812 Brentuximab vedotin CD30 MMAE valine citrulline; Seattle Genetics Adcetris approval.

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Immunological Applications

Antibody–drug conjugates (ADCs) combine:

Antibody-drug conjugates integrate precision of biologics with potency of small molecules to overcome poor therapeutic window of conventional chemotherapy that diffuses into all tissues causing systemic toxicity. Monoclonal antibody component provides tumor-selective homing through high affinity binding Kd 10^-9 to 10^-11 M to antigens preferentially expressed on malignant cells ten to hundred fold over normal tissues, such as HER2, CD30, CD22, and internalization via receptor mediated endocytosis clathrin dependent trafficking to early endosome then late endosome fusing with lysosome pH 4.5 containing cathepsins B and L. Chemical linker connecting payload determines release kinetics: cleavable valine-citrulline dipeptide sensitive to lysosomal cathepsin B with PABC self-immolative spacer, acid-labile hydrazone stable at neutral pH 7.4 but hydrolyzes at pH below 6.0, disulfide sensitive to cytosolic glutathione 1000 fold higher than plasma. Non-cleavable thioether linker SMCC requires complete proteolytic degradation of antibody backbone to release lysine-MCC-drug metabolite still active. This mechanistic insight supports diagnostic and therapeutic applications while reinforcing core immunological and cell biology principles taught in advanced curricula.

Ref: Beck et al Nat Rev Drug Discov 2017 16:315 ADC linker payload MMAE DM1; Trail Cancer Immunol Res auristatin maytansine.

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Immunological Applications

Which toxin is commonly used in immunotoxins?

Selecting optimal toxin component for immunoconjugate involves potency, intracellular stability, lack of mammalian cell surface receptors to avoid nonspecific uptake, and ability to produce recombinant fusion maintaining disulfide integrity. Diphtheria toxin secreted by toxigenic Corynebacterium diphtheriae, 58 kDa single polypeptide proteolytically cleaved into 21 kDa catalytic A fragment and 37 kDa binding-translocation B fragment linked by single disulfide Cys186-Cys201. Catalytic activity transfers ADP-ribose to elongation factor 2 with turnover number approximately 1000 per minute. Native receptor heparin binding EGF-like precursor widely expressed, so receptor-binding domain residues 1-389 deleted to generate DT388 retaining translocation domain helices capable of endosomal membrane insertion at acidic pH after furin cleavage. Similarly Pseudomonas exotoxin A 66 kDa secreted by Pseudomonas aeruginosa, ADP-ribosylates EF2 after binding CD91 receptor, truncated to PE38 removing domain Ia binding region retaining domain II translocation and domain III catalytic with C-terminal REDLK endoplasmic reticulum retrieval motif. Plant toxins like ricin A chain or gelonin inactivate ribosomes via depurination but require chemical conjugation via heterobifunctional crosslinkers SPDP forming disulfide bridge.

Ref: Weldon & Pastan FEBS J 2011 PE38 DT388 catalytic domain; Collier EF2 ADP-ribosylation translation arrest mechanism.

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Immunological Applications

Immunotoxins kill target cells mainly by:

Mechanism by which protein toxins arrest protein synthesis culminates in rapid programmed cell death via mitochondrial pathway capable of killing quiescent cells. Diphtheria toxin fragment A catalyzes ADP-ribosylation of unusual post-translationally modified histidine diphthamide at position 699 of eukaryotic elongation factor 2 present exclusively on domain IV, using oxidized NAD+ as ADP-ribose donor releasing nicotinamide. Modified elongation factor cannot mediate translocation step of peptidyl-tRNA from A site to P site on 60S ribosomal subunit, halting elongation after single round. Ricin A chain functions as RNA N-glycosidase hydrolyzing N-glycosidic bond of adenine 4324 in 28S ribosomal RNA alpha sarcin-ricin loop critical for EF2 GTPase activation, depurinating single base rendering 60S subunit unable to bind elongation factors. Both events cause accumulation of stalled ribosomes triggering ribotoxic stress response via MAP3K ZAK activating JNK and p38, plus depletion of short-lived anti-apoptotic proteins Mcl-1 half-life thirty minutes, XIAP, c-FLIP required to restrain caspase cascade, tipping balance toward Bax Bak oligomerization forming mitochondrial outer membrane pores releasing cytochrome c, Smac DIABLO, formation of Apaf-1 apoptosome activating initiator caspase 9 then executioners caspase 3 and 7 cleaving PARP leading to chromatin condensation within hours even in nondividing cells resistant to mitotic inhibitors.

Ref: Collier Annu Rev Biochem 1975 diphtheria ADP-ribosyl EF2; Olsnes Pharmac Ther ribosome N-glycosidase ricin apoptosis.

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