Cellular Immune Response I

Cellular Immune Response I

• The lecture is about Cellular Immune Response I, specifically T lymphocytes responses.
• The writer is Ali Aljaziri and the reviewer is Faisal Aloraifi.
• The lecture covers the main phases of T lymphocyte responses.
• Antigen recognition by T lymphocytes, and the role of CD4, CD8, and adhesion molecules were discussed.
• Activation signals and co-stimulation molecules for CD4+ T lymphocytes were also detailed.
• The activation process of CD8+ T lymphocytes was explained.
• The functional responses and relevance of activated T lymphocytes were explored.
• Characteristics of memory T lymphocytes and the endpoint of the cellular immune response were covered.
• The migration of effector T lymphocytes to the infection site was discussed.
• The lecture covers various types of intracellular microbes combated by T cell-mediated immunity.
• T lymphocytes play a major role in cell-mediated immunity (CMI).
• CMI defends against infections by intracellular microbes through two types of infections.
• Firstly, phagocytes ingest microbes as part of the innate immune response.
• Some microbes resist phagocytosis.
• Pathogenic intracellular bacteria and protozoa survive and replicate within phagocytic vesicles.
• Viruses infect and replicate within the cytoplasm of cells.
• Examples of intracellular microbes were given (Mycobacteria, Listeria, Legionella, Cryptococcus, Leishmania, Trypanosoma, Plasmodium, Cryptosporidium, all Rickettsiae, and all viruses).

Lecture Outline

• The lecture outlined several topics including main phases of T lymphocytes responses
• Antigen recognition and role of CD4, CD8, and adhesion molecules.
• Activation signals and co-stimulation molecules for CD4+ T lymphocytes.
• Activation process of CD8+ T lymphocytes.
• Functional responses and relevance of activated T lymphocytes.
• Memory T lymphocytes and the endpoint of the cellular immune response.
• Migration of effector T lymphocytes to the infection site.

Importance

• The doctor emphasized that every objective is a question and the student should know the answer.
• The information contained was crucial for T-cell activation and function.

T-cell Activation

• T cells recognize antigens with TCR, CD3, and zeta protein.
• APC surface molecules (MHC I or II) are important for T-cell recognition.
• Important surface molecules from T-cells and corresponding ligands were explained.
• CD28 is a co-stimulatory receptor;
• CTLA-4 and PD-1 are inhibitory receptors on T cells.
• Co-receptors (CD4 or CD8) help stabilize interactions (signal 1) with MHC-associated peptide antigens.

Costimulation

• Costimulatory signals (signal 2) between cells is essential to prevent false alarms.
• T-cell activation requires a reciprocal and sequential signal 2 exchange between cells.
• A T-cell-APC interaction begins with TCR interaction with peptide/MHC complex.
• Signals, including cytokines, control T-cell differentiation (signal 3).
• The absence of co-stimulatory molecules causes T-cell anergy or apoptosis.

CD8 T-cell Activation

• CD8+ T cells are activated by APCs (dendritic cells).
• Infected tissue cells can also activate CD8+ T cells or function as a presentation site.
• Helper T cells play a crucial role in activating CD8 T-cells
• Cytokines from helper T cells promote CD8+ T cell differentiation/expansion.

Activation Pathways

• The biochemical pathway that connects antigen recognition with T-cell responses involves enzyme activation, adaptor protein recruitment, and transcription factor production.
• These pathways are initiated when the TCR interacts with MHC on APCs.

Memory T lymphocytes

• Memory T cells persist long after an infection is cleared.
• They are important for rapid immune responses upon re-exposure.
• Central memory cells reside in lymphoid organs and promote rapid expansion while effector memory cells are present at infection sites.

Effector T Cell Migration

• Naive T cells migrate through the bloodstream and lymphoid tissues.
• Effector T cells migrate to infection sites (specific to antigen).
• Adhesion molecules (L-selectin, Integrin) and chemokine receptors (CCR7) help with migration.
• T cell migration to the infection site is independent of antigen recognition.

Functional Responses

• Cytokine production
• Clonal expansion
• Differentiation into effector cells
• Differentiation of naïve CD4 T cells into effector cells (Tfh, Th1, Th2, Th17).
• Memory T cells also help with elimination of microbes via other mechanisms in addition to effector cells.

End Point of Cellular Immune Response

• The immune system returns to homeostasis.
• Excess T cells are eliminated through apoptosis.
• Only memory cells remain for quick response to future infections.