Immunology for Medicos/USMLE Step 1/Boards

Evaluate monoclonal antibodies for high specificity and consistency in a serum assay, as they bind a single epitope; contrast with polyclonal antibodies’ multiple epitopes for broader detection.

Explore how engineered antibody fragments such as single-chain variable fragments (scFv) and VH domains enable targeted cancer immunotherapy by enhancing tumor specificity and tissue penetration while reducing systemic toxicity.

Explore how opsonization and phagocytosis mark pathogens for destruction, detailing IgG and FC receptor interactions, and show how C3 deficiency impairs opsonization in children with encapsulated infections.

Explain how opsonization marks pathogens with IgG and C3 to boost phagocytosis by macrophages and neutrophils, and how C3 deficiency disrupts this, causing recurrent infections with encapsulated bacteria.

Dendritic cells and macrophages act as antigen presenting cells recognizing pathogen associated molecular patterns via toll like receptors, triggering nfkb signaling and activation of T and B cells.

Explore how naive CD4 T cells differentiate into Th1 or Th2 under IFN-γ/IL-12 and IL-4, linking Th1 to intracellular defense and Th2 to IgE-mediated allergy.

Learn how thymic T cell maturation proceeds from double-positive progenitors through positive and negative selection in the cortex and medulla, generating CD4+ and CD8+ T cells.

Explore th1 and th2 t cell subsets and their roles in cell-mediated and humoral immunity, including il-2, interferon gamma, il-4, and responses to intracellular and extracellular pathogens.

Foxp3 encodes a transcriptional regulator essential for regulatory T cell development and function. It suppresses immune activation through IL-10, Tgfb, and CTLA-4, preventing autoimmunity as seen in Ipex syndrome.

Foxp3 drives regulatory T cell development and suppresses immune activation via IL-10, TGF-beta, and CTLA-4. Foxp3 mutations cause IPEX syndrome with autoimmunity, including enteritis, dermatitis, and type 1 diabetes.

Explore regulatory T cells (Tregs) and how CD4+ CD25+ Foxp3+ cells maintain immune homeostasis using IL-10, TGF-β, and CTLA-4, with implications for autoimmunity, transplantation, and cancer.

Explore adenosine deaminase deficiency, its impact on purine metabolism, and how datp accumulation causes lymphocyte apoptosis and severe immunodeficiency.

Understand chronic granulomatous disease, an NADPH oxidase defect, with recurrent catalase-positive infections and granulomas, and learn its overview, diagnostic flow cytometry, nitroblue tetrazolium testing, and treatment implications.

Identify how a low CH50 with a normal RH50 signals a classical pathway deficiency, most likely C1, explaining susceptibility to encapsulated bacterial infections.

Explore Hyper-IgE syndrome, an autosomal dominant immunodeficiency, and explain how Jak-STAT signaling defects impair Th17 function and neutrophil chemotaxis, causing eczema and recurrent infections.

Hyper-IgM syndrome caused by a CD40 ligand mutation disrupts CD40-CD40L interactions, impairing B cell class switching and leading to low IgG/IgA and recurrent infections.

Explore primary immunodeficiency disorders through a clinical case of ataxia telangiectasia, highlighting progressive ataxia, telangiectasias, recurrent infections, and ATM gene-related DNA repair defects.

Explore severe combined immunodeficiency, a genetic T and B cell deficiency often X-linked or autosomal, with infancy infections like Pneumocystis pneumonia, failure to thrive, diarrhea; stem cell transplant may cure.

Explore Wiskott-Aldrich syndrome features—eczema, recurrent infections, thrombocytopenia with small platelets, low IgM, and elevated IgE—along with X-linked inheritance and cytoskeletal dysfunction.

Explore x-linked agammaglobulinemia (XLA), a BTK mutation blocking B cell maturation, causing pan-hypogammaglobulinemia with absent CD19+ B cells and recurrent infections; manage with immunoglobulin replacement and avoid live vaccines.

Uncover X-linked agammaglobulinemia pathophysiology from BTK mutations blocking B cell maturation, causing low immunoglobulins, absent CD19+ B cells, recurrent sinopulmonary infections, and immunoglobulin replacement therapy.

Examine type four hypersensitivity and cellular immunity through a Candida skin test, highlighting Th1 differentiation, IFN-γ production, macrophage activation, and induration as a positive response.

Identify anaphylaxis from a peanut-triggered case and administer intramuscular epinephrine as first-line treatment, followed by emergency care and monitoring.

Examine angioedema etiologies, focusing on mast cell activation and bradykinin pathways, especially ace inhibitor–induced bradykinin-mediated swelling. Differentiate allergic from bradykinin angioedema and review treatments for potentially life-threatening airway involvement.

Explore how latex exposure triggers type I hypersensitivity through Th2-driven IL-4 mediated IgE production, mast cell degranulation, and resulting itching, redness, and swelling.

Explore latex allergy immunology, detailing antigen presenting cells, Th2 responses with IL-4 and IL-5, IgE production, and mast cell–mediated symptoms in healthcare workers.

Explore type one hypersensitivity as IgG-mediated and IgE-driven processes with mast cell degranulation. Analyze a bee sting case to illustrate sensitization, IL-4 driven IgE production, and histamine-mediated redness.

Atopic dermatitis involves a Th2-skewed immune response driven by IL-4 and IL-13, with IgE production and skin-barrier dysfunction in flexural regions.

Explore how horse-derived polyclonal antivenom can trigger serum sickness, a type three hypersensitivity, through immune complex deposition after venom antivenom therapy.

Explore how anti-PD-1 and anti-CTLA-4 checkpoint inhibitors reinvigorate T cells to treat melanoma with high PD-L1 expression, featuring pembrolizumab and nivolumab.

Explore cancer immunotherapy targeting PD-1/PD-L1 to unleash cytotoxic T cells and fight tumors, with monoclonal antibodies like pembrolizumab, nivolumab, and atezolizumab.

Conjugate vaccines link polysaccharide sugars to a protein to engage T helper and memory B cells, providing long lasting immunity in young children.

Explore Haemophilus influenzae type b vaccines and why polysaccharide vaccines fail in infants. The Hib conjugate vaccine uses a protein carrier to elicit a T cell-dependent response and memory.

Explore immunotherapy fragment options, focusing on Fab fragments that bind tumor antigens without triggering complement activation or Fc-mediated phagocytosis, contrasting with Scfv and single-domain antibodies.

Explore how rituximab, a monoclonal antibody targeting CD20 on B cells, depletes B cells through complement-mediated lysis, antibody dependent cellular cytotoxicity, and phagocytosis in autoimmune diseases and lymphomas.

Explore granulomatosis with polyangiitis (GPA) as a vasculitis and learn how cytokine inhibitors, T cell costimulation inhibitors, and B cell depletion strategies modulate the immune system to reduce inflammation.

Explore how glucocorticoids like fluticasone treat allergic rhinitis by inhibiting phospholipase A2, reducing pro-inflammatory cytokines, and decreasing nasal mucosal edema and mucus production.

Glucocorticoids suppress inflammation by inhibiting NF-kB and modulating cytokine production, upregulating annexin one to block phospholipase A2, reduce leukocyte migration, and promote eosinophil apoptosis.

Examine hyperacute rejection in kidney transplants, a type II hypersensitivity caused by preformed anti-HLA or anti-ABO antibodies that trigger complement and immediate graft loss.

Analyze a one-week post-lung transplant case to identify acute rejection caused by a cell-mediated response against donor HLA. Compare hyperacute, acute, and chronic rejection mechanisms and their lung-specific features.

Examine the three transplant rejection types—hyperacute, acute, and chronic—covering onset, etiology, and graft morphology in kidney transplants, with a hyperacute case highlighting preformed antibodies.

Explore the immunologic spectrum of lung transplant rejection, from hyperacute to chronic, focusing on bronchiolitis obliterans and an obstructive spirometry pattern that guides management with optimized immunosuppression or retransplantation.

Explore the mechanism of sirolimus in organ transplantation, showing how it binds FKBP and inhibits mTOR to block IL-2 signaling in a kidney transplant immunosuppression context.

Explore how common immunosuppressants prevent t cell activation by inhibiting calcineurin or mTOR, and how nucleotide synthesis blockers curb lymphocyte proliferation.

Explore the pathophysiology of acute graft-versus-host disease after allogeneic hematopoietic stem cell transplantation, highlighting donor T cell activation, cytokine release, and tissue attack on skin, liver, and gut.

Explore the immune defense against mycobacterial infections, detailing interleukin-12, interferon-gamma signaling, phagolysosome fusion, and granuloma formation, and discuss autosomal recessive IFN-γ receptor deficiency causing recurrent infections despite BCG vaccination.

Eosinophils kill parasites by releasing granule proteins and reactive oxygen species after IgG-coated parasites engage Fc receptors. Deficient eosinophil counts would weaken the body's ability to defend against helminth infections.

Eosinophils defend against parasites via antibody dependent cell mediated cytotoxicity and drive allergic asthma by releasing inflammatory mediators like prostaglandins and leukotrienes, linking elevated eosinophils to wheezing.

Parapneumonic effusions arise from exudative pleural fluid in bacterial pneumonia, reflecting inflammation in the pleural space. Leukotriene B4, a potent chemotactic eicosanoid, elevates to recruit neutrophils there.

Explore how the polysaccharide capsule drives virulence in encapsulated bacteria and how C5–C9 defects impair MAC formation, raising meningitis risk from Neisseria and Streptococcus pneumoniae.

Explore how IL-12 directs naive T cells to become Th1 cells, activating macrophages and IFN-γ against intracellular pathogens. Identify IL-12 receptor deficiency impairs Th1 response, increasing susceptibility to severe infections.

Explain how IL-12 from infected macrophages activates T cells and NK cells to produce IFN-γ, which signals via JAK1/JAK2–STAT1 in macrophages to enhance intracellular killing against Mycobacterium tuberculosis.

Interferon gamma release assays measure T cell responses to Mycobacterium tuberculosis antigens in a blood test and aid latent TB infection diagnosis, with no BCG cross-reactivity and a single visit.

Interferons alpha and beta bind to neighboring cells to induce antiviral proteins that degrade viral RNA and halt protein synthesis, creating an antiviral state for use in infections and cancers.

Type one interferons (IFN-α and IFN-β) activate autocrine signaling to halt viral replication. They induce antiviral proteins like RNAs L and PKR that degrade viral RNA and halt protein synthesis.

The lecture explains how sepsis triggers a cytokine storm driven by tnf-alpha, with il-1 and il-6 fueling inflammation, vascular permeability, and systemic shock.

Examine vaccine-related vasovagal syncope and anaphylaxis through a clinical case, highlighting triggers, mechanisms, clinical features, and management, including supine positioning and epinephrine.

Explore how aging impairs vaccine responses through immunosenescence, including telomere shortening, reduced naive lymphocytes, and inflammation that dampens the adaptive immune response.

Explore the extrinsic pathway of apoptosis via Fas-FasL, its role in preventing autoimmunity, and how impaired Fas-mediated apoptosis contributes to SLE by allowing autoreactive T cells to persist.

Morbilliform drug eruption is a type iv hypersensitivity causing itchy erythematous macules and papules 5–21 days after starting a drug; stop the offending drug and expect resolution in 1–3 weeks.

Explain urushiol-induced contact dermatitis as a type iv hypersensitivity, detailing sensitization and elicitation phases, hapten-protein complexes, Langerhans cell transport, and CD4/CD8 T cell–mediated keratinocyte damage.

Explore systemic lupus erythematosus manifestations through lab findings like hemolytic anemia, thrombocytopenia, leukopenia, and low C3/C4 from immune complex formation, with anti-dsDNA as the most specific diagnostic antibody.

Identify how autoantibodies in SLE cause hematologic abnormalities, including autoimmune hemolytic anemia, thrombocytopenia, and leukopenia, and how immune complex deposition drives lupus nephritis with proteinuria.