Immunology Fall 2026: Lecture 7 Cellular Innate Immunity Part 3/Antigens and Antibodies

Overview

Innate immune sensors tailor responses to pathogens: NLR proteins can assemble inflammasomes that activate caspase-1, IL-1β, and pyroptosis, while cGAS-STING drives IRF-dependent type I interferon. The lecture then traces adaptive immunity from von Behring and Kitasato’s rabbit serum-transfer experiments to antibodies: Y-shaped immunoglobulins bind specific antigen epitopes, a specificity illustrated by Karl Landsteiner’s chemical studies and the multiple antibody targets on SARS-CoV-2 spike.

Key takeaways

NLRP3 inflammasomes assemble with ASC and activate caspase-1, linking pathogen or danger sensing to IL-1β production and inflammatory pyroptosis.
Apoptosis and pyroptosis use different caspases and have different immune consequences: caspase-3-associated apoptosis is relatively contained, while caspase-1-associated pyroptosis promotes inflammation.
The von Behring–Kitasato rabbit experiments showed both specificity and transferability: serum from a C. botulinum-exposed rabbit protected another rabbit from C. botulinum, but not from C. tetani.
Passive antibody therapy applies the serum-transfer principle by supplying pre-made antibodies, including laboratory-produced antibodies and antibody preparations used against toxins and infections.
An antibody binds an epitope rather than an entire antigen; the lecture cites at least 20 antibody epitopes on SARS-CoV-2 spike, allowing mutations at one site to leave other targets intact.

Chapters

0:00 Pattern-Recognition Receptors Tailor Innate Responses

Pattern-recognition receptors (PRRs) detect different microbial features and help direct an immune response appropriate to the pathogen.
Toll-like receptors (TLRs), RIG-I-like receptors (RLRs), and C-type lectin receptors (CLRs) are families, not single receptors.
The lecture transitions from previously covered PRRs to NOD-like receptor-related proteins and their roles in cellular innate immunity.

4:10 NLR Protein Domains and Their Evolutionary Parallels

NLR commonly refers to nucleotide-binding domain and leucine-rich repeat-containing proteins, with a central nucleotide-binding domain, a leucine-rich repeat region, and a variable third domain.
NLR subfamilies include NLRP proteins, which have a pyrin domain, and NLRC proteins.
Related protein architectures occur in plant NBS proteins and the mammalian apoptosis protein APAF-1.

9:30 From APAF-1 Apoptosome to NLR Inflammasome

In apoptosis, cytochrome c helps APAF-1 form the apoptosome, which activates caspase-3 and promotes cell death.
NLRP3 and the adaptor ASC can assemble a structurally similar complex called the inflammasome.
Unlike the apoptosome, the inflammasome activates caspase-1 and drives inflammatory processes rather than apoptosis.

15:30 Caspase-1 Links Inflammasomes to Pyroptosis

Apoptosis is presented as relatively quiet cell death: cells shrink and form membrane-bound fragments that contain cellular contents.
Pyroptosis is inflammatory, or “loud,” cell death that can alert neighboring cells to danger and is often associated with infection.
Inflammasome activation leads to caspase-1 activity, IL-1β production, and pyroptosis; gasdermin D helps disrupt the cell.
The lecture contrasts caspase-1 in inflammasome responses with caspase-3 in the apoptosome pathway.

23:08 NLR Triggers and Inflammation-Related Disease

NLR-associated inflammasome activation can follow detection of microbial material and signals such as excess ATP, cholesterol, uric acid crystals, asbestos, and silica.
Mutations affecting inflammasome components are associated with autoinflammatory syndromes, including familial Mediterranean fever and cryopyrin-associated periodic syndromes (CAPS).
Inflammasome activity has also been investigated in conditions including inflammatory bowel disease, type 2 diabetes, Alzheimer’s disease, and atherosclerosis.

26:55 cGAS-STING Senses Cytoplasmic DNA and Induces Interferon

Cytoplasmic cGAS can detect DNA, produce a small signaling molecule, and activate STING.
STING signaling activates IRF transcription factors, leading to type I interferon production in response to viral DNA.
The cGAS-STING pathway is being studied as a target for therapies that modulate inflammation; related cGAS-like systems have also been identified in other organisms.

31:50 Anti-Inflammatory Medicines and Innate Immunity

Inflammatory cytokines, including TNF, IL-6, and type I interferons, contribute to symptoms such as fever, lethargy, muscle pain, and nausea.
NSAIDs such as ibuprofen and aspirin suppress inflammatory pathways, while corticosteroids can inhibit both innate and adaptive immune responses.
Acetaminophen (Tylenol) is described primarily as acting through the central nervous system to reduce symptoms rather than suppressing inflammation in the same way.
Studies of ibuprofen use around COVID-19 vaccination have produced mixed results; some suggest a potentially reduced adaptive response, but the evidence is not definitive.

38:43 Adaptive Immunity Adds Specificity After Innate Defenses

Innate immune components respond early, but persistent microbes can require the slower adaptive response.
Adaptive immunity adds strong specificity and includes B cells, antibodies, and T cells.
The lecture introduces adaptive immunity through historical experiments that helped identify protective factors in blood.

41:00 von Behring and Kitasato’s Rabbit Experiments

In the 1890s, Emil von Behring and Shibasaburo Kitasato studied protection against Clostridium botulinum, Clostridium tetani, and Corynebacterium diphtheriae.
Rabbits given a low dose of one pathogen survived, while rabbits given a high dose without prior exposure died.
The experiments established a model for testing whether prior exposure could protect against a later, otherwise lethal dose.

44:00 Prior Exposure Produces Pathogen-Specific Protection

A rabbit first exposed to a low dose of C. botulinum survived a later high dose of C. botulinum.
That protection did not extend to C. tetani, despite the bacteria belonging to the same genus; the rabbit died after the mismatched challenge.
The experiments demonstrated that adaptive protection is specific to the pathogen that prompted the initial response.

50:25 Serum Transfer Identifies a Protective Blood Factor

von Behring and Kitasato compared serum—the liquid portion of blood—with spleen cells from a previously exposed rabbit.
They transferred each sample into new rabbits and challenged them with a high dose of C. botulinum.
Recipients of serum survived, while recipients of spleen cells died, showing that the transferable protective factor was in the blood’s liquid fraction.

54:00 Passive Antibody Therapy Applies the Serum-Transfer Principle

Passive antibody therapy gives a patient antibodies produced by another organism or made in a laboratory; the recipient does not generate the initial antibody response.
Antibody preparations have been used for exposures including rabies, tetanus, botulism, snake venom, and black widow spider venom.
During the early COVID-19 pandemic, convalescent plasma supplied antibodies from people who had recovered; laboratory-made antibodies were also used as treatments.

58:20 Gamma Globulin and the Y-Shaped Antibody Structure

Researchers found that the protective serum factor was a protein and localized activity to the gamma-globulin fraction of blood proteins.
The historical names gamma globulin and immunoglobulin remain in use; IVIG means intravenous immunoglobulin.
Antibodies have a Y-shaped structure with two identical antigen-binding arms, called Fab regions, and a constant Fc region.

1:05:10 Antigens, Epitopes, and Landsteiner’s Chemical Specificity

An antigen is a molecule recognized by the adaptive immune system; antibodies can recognize proteins, carbohydrates, nucleic acids, lipids, and other compounds.
Karl Landsteiner showed that antibodies could distinguish closely related synthetic chemicals, demonstrating specificity for subtle chemical differences.
An epitope is the particular portion of an antigen that an antibody contacts, and one antigen can contain multiple epitopes.
Antibody epitopes are not restricted to proteins, unlike the more limited forms of antigen recognition discussed for T cells.

1:11:40 SARS-CoV-2 Spike Has Multiple Antibody Epitopes

COVID-19 vaccines expose the immune system to SARS-CoV-2 spike rather than the entire virus.
Research discussed in the lecture has identified at least 20 antibody epitopes on spike, so the response can include antibodies directed at many distinct targets.
A mutation affecting one epitope may disrupt antibody binding at that site without eliminating recognition of the other spike epitopes.

Summary, takeaways, and chapters were generated by AI from the video's transcript and may contain errors. The video belongs to its creator, Brianne Barker.