Main subpopulations and receptors
The development of cellular immunity is linked to the discovery of key lymphocytes in the 1970s. Killer T cells mediate graft rejection and combat viruses, whereas suppressor T cells dampen excessive responses to self-antigens. Later, natural killer (NK) cells were described; while functioning within the innate immune system, they utilize similar cytolytic mechanisms.
The recognition process is based on TCR (T-cell receptors). Studies by R. Zinkernagel and P. Doherty proved that T lymphocytes do not recognize the free pathogen itself, but rather its peptide embedded in major histocompatibility complex (MHC) molecules. The diversity of these receptors is achieved through genetic rearrangement of DNA segments.
Cytotoxic response and its stages
The antigen-specific cytotoxic response develops sequentially:
- Activation: Dendritic cells present foreign peptides to naive lymphocytes.
- Proliferation: Interleukin-2 (IL-2)-dependent division of activated cells.
- Differentiation: Maturation of lymphocytes into mature cytotoxic T lymphocytes (CTLs).
- Effector phase: Direct destruction of target cells.
Unlike MHC-II, MHC-I molecules are expressed on the surface of all nucleated cells in the body. The CD8 coreceptor binds to these molecules, determining the specificity of CTLs.
Comparison of natural and immune cytolysis
Fundamental differences exist between the innate response of NK cells and the adaptive response of killer T cells:
| Sign | Natural cytolysis | Immune cytolysis |
|---|---|---|
| Effectors | NK cells | CD8+ T lymphocytes |
| Targets | Stress-induced molecules | Peptide complexed with MHC-I |
| Clonality | Absent | Present |
| Memory | Not formed | Formed |
| Mechanisms | Perforins, granzymes | Perforins, granzymes, Fas-mediated apoptosis |
Antiviral defense and memory
Antiviral defense relies on four components: type I interferons, NK cells, cytotoxic T lymphocytes, and neutralizing antibodies. Primary contact leads to the generation of specialized memory cells.
Upon re-exposure to the same virus, these cells mount a rapid secondary response. Antigen presentation is accelerated, antiviral antibody production is enhanced, interferon-gamma production increases, and killer cells are activated, resulting in protective immunity.
Killer T cells operate strictly by the book: the passport is MHC-I, and the visa is CD8.
Class and exam questions
What is the main difference between cytotoxic T cells and NK cells?
NK cells belong to innate immunity, lack clonal specificity and memory, and recognize stress-induced molecules. Cytotoxic T cells possess strict antigen specificity, require presentation via MHC class I, and form long-term immunological memory.
What role do MHC-I molecules play in the body?
MHC-I molecules are present on all nucleated cells and serve as a "display window" for intracellular peptides. If a cell is infected by a virus, CD8+ T lymphocytes recognize this complex and trigger contact-mediated lysis.
What stages comprise the cytotoxic immune response?
The response proceeds through four stages: activation by dendritic cells, IL-2-dependent proliferation, differentiation into mature CTLs, and the effector phase resulting in target destruction.
What else to study on this topic
- Hybridoma technology and the production of monoclonal antibodies
- Genetics of antibody and TCR diversity according to S. Tonegawa
- Mechanisms of antigenic variation in malaria (sporozoite stage and VSAs)
- The role of cytokines (including IFN-γ) in macrophage activation
- Mechanisms of immune response limitation and regulatory T cells
Master the entire topic in the "Immunology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Cellular Immunity" and 723 other pages on the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 23 video lessons on the subject
Other topics in the "Adaptive Immunity" section
The entire "Adaptive Immunity" sectionPrepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.