Cellular Immune Response II

Cellular Immune Response II

• Cellular immunity (CMI) defends against intracellular microbes
• T lymphocytes mediate CMI
• Some T lymphocytes activate phagocytes to destroy ingested microbes
• Other T lymphocytes kill infected host cells harboring microbes in the cytoplasm

Types of CMI Killing Microorganisms

• Involves CD4+ and CD8+ T lymphocytes
• These cells work together to eliminate different types of microbes

Types of CD4+ Helper T Cells

• Different types of CD4+ helper T cells exist (Th1, Th2, Th17, and others)
• Mechanisms determine their differentiation
• Certain cytokines drive the differentiation of T cells
• The types of cells promote different immune responses

Role of CD4+ Th1 Lymphocytes

• Th1 cells target intracellular pathogens
• They help macrophages fight off the intracellular microbes

Delayed Hypersensitivity

• A form of hypersensitivity, taking 24-72 hours to develop after exposure to an antigen.
• Delayed hypersensitivity is mediated by T cells, rather than antibodies

Role of CD4+ Th2 Lymphocytes

• These cells combat helminths (e.g., parasitic worms)

Ways CD8+ Effector T Lymphocytes Kill Infected Cells

• CD8+ cytotoxic T lymphocytes (CTLs) recognize infected cells carrying a specific intracellular microbe.
• CTLs then kill the infected cells
• CTLs use cytotoxic mechanisms, including releasing granzymes and perforin into the infected cell to induce apoptosis

Features of Regulatory T Lymphocytes

• Regulatory T lymphocytes (Tregs) suppress CMI
• They help maintain immune balance

Characteristics of Subsets of CD4 Helper T Cells

• Th1 cells release interferon-γ (IFN-γ) and target macrophages for intracellular pathogens, such as mycobacteria
• Th2 cells release cytokines like IL-4, IL-5, and IL-13 and combat parasites of helminths.
• Th17 cells combat extracellular pathogens, like bacteria and fungi
• Cytokines released from these cells trigger different inflammatory and immune response

General Properties of T Cell Cytokines

• T cell cytokines are transient responses to antigens.
• Cytokines usually act on the same cells that produce them or nearby.
• T cell cytokines have pleiotropic effects.
• T cell cytokines have redundancy.

Biological Actions of Selected T Cell Cytokines

• Different cytokines influence T cell proliferation, differentiation, and action.
• Some cytokines activate macrophages.
• Cytokines are necessary to activate other types of immune cells

Functions of Th1 CD4+ Effector T Lymphocyte

• Stimulate the production of antibodies to promote phagocytosis of microbes.
• Killing of microbes via the production of interferon (IFN) as a crucial component of cell-mediated immunity

Role of Th1 Cells in Defense Against Intracellular Pathogens

• Th1 cells activate macrophages in response to intracellular pathogens, resulting in bacterial killing
• These cells stimulate the production of several cytokines, including TNF and IFN

What is Delayed Hypersensitivity?

• An immune reaction taking 24-72 hours to develop after antigen exposure.
• It's mediated by T cells rather than antibodies

Mechanism Determining the Direction of Activated CD4+ T Cell Differentiation

• Pathogen type
• Cytokine from antigen presenting cells (APCs)
• Activation of transcription factors determines the direction of differentiation for T cells.
• Cytokine production from the effector cells

Role of Th2 Cells in Defense Against Helminths

• Th2 cells stimulate phagocytic cells like eosinophils, which fight against parasitic worms/helminths
• They also mediate antibody production (especially IgE) to combat helminthic infections

Classical & Alternative Macrophage Activation

• Macrophages play a crucial role in innate and adaptive immunity and can be activated in two ways:
• Classical activation (M1): activated by microbial products, resulting in inflammation.
• Alternative activation (M2): stimulated by cytokines that promote tissue healing, such as IL-4 or IL-13

Balance Between Th1 & Th2 Cell Activation

• The balance between Th1 and Th2 cell activation affects the outcome of intracellular infections.
• Th1 cells activate phagocytes to eliminate microbes, while Th2 cells inhibit classical macrophage activation.

Uncontrolled Mycobacterium Leprae

• Leads to lepromatous leprosy, characterized by uncontrolled bacterial growth.

How Can CD8+ Effector T Cells Kill Infected Cells?

• CD8+ T cells interact with infected cells
• These cells release granzymes and perforin to induce apoptosis
• This eliminates harmful reservoirs of infection

Cooperation Between CD4+ and CD8+ T Cells

• CD4+ T helper cells regulate and interact with CD8+ cytotoxic T Lymphocytes, assisting in the immune response towards infections.
• Cooperation between these cells efficiently eradicates infected cells.

What are Regulatory T Lymphocytes?

• Regulate T lymphocytes (Tregs) help to control and balance immune responses through their role in suppressing the immune system when necessary to maintain a healthy state.
• CTLA4 inhibits immune responses and shut down T cell responses

Explore the intricate mechanisms of cellular immunity, focusing on the roles of T lymphocytes in defending against intracellular microbes. This quiz covers the types of T cells, their functions, and the process of delayed hypersensitivity. Test your understanding of these critical aspects of the immune system.