Immune Response and Helper T Cells

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Questions and Answers

What is the main role of CD40L in the immune response?

Engaging with CD40 on macrophages and B cells to activate them (correct)

Inhibiting the proliferation of virus-infected cells

Directly killing infected cells

Stimulating the production of Ig-E by plasma cells

Which cytokine is specifically associated with the activation of macrophages by TH1 cells?

IFN-y (correct)

TNF

IL-4

IL-10

What is the role of IL-5 in the immune response?

Increasing macrophage cytokine production

Stimulating T cell differentiation

Activating eosinophils (correct)

Promoting B cell proliferation

Which of the following cytokines limits and terminates immune responses?

TGF-b Signup and view all the answers

What type of immune cell do TH2 cells induce the activation of through the 'alternative pathway'?

Macrophages Signup and view all the answers

Which major source produces cytokines in an innate immune response?

Macrophages Signup and view all the answers

Which population of T cells is primarily responsible for secreting cytokines during adaptive immune responses?

CD4+ T lymphocytes Signup and view all the answers

What do colony-stimulating factors (CSFs) stimulate?

Formation of blood cell colonies from bone marrow Signup and view all the answers

What effect do TH17 cells have on neutrophils and monocytes?

They recruit them and enhance their activity Signup and view all the answers

How do activated CD8+ T lymphocytes contribute to combating infection?

By differentiating into cytotoxic T lymphocytes that kill infected cells Signup and view all the answers

What is the primary role of B cells in the immune response?

To secrete antibodies as plasma cells Signup and view all the answers

Which statement best describes the role of natural killer (NK) cells?

They kill stress-damaged or infected cells. Signup and view all the answers

What characterizes Type II hypersensitivity reactions?

IgG and IgM antibodies promote phagocytosis and tissue injury. Signup and view all the answers

What are antigen presenting cells (APCs) primarily responsible for?

Transporting and displaying antigens for lymphocyte recognition Signup and view all the answers

Which organ is NOT classified as a generative lymphoid organ?

Lymph nodes Signup and view all the answers

Type I hypersensitivity disorders are primarily characterized by which mechanism?

TH2 cell activation and mast cell involvement Signup and view all the answers

What manifests as inflammation in the early reaction to microbes?

Epithelial barriers and phagocytic activity Signup and view all the answers

Which of the following best defines Type III hypersensitivity?

Formation and deposition of antigen-antibody complexes in tissues Signup and view all the answers

What is the primary cause of acute serum sickness?

Administration of large amounts of proteins Signup and view all the answers

Which component of the immune response is primarily involved in the formation of immune complexes?

Antibodies Signup and view all the answers

Which disease is associated with immune complexes formed from nuclear antigens?

Systemic lupus erythematosus (SLE) Signup and view all the answers

What role do activated TH17 cells play in immune responses?

Secrete IL-17 and recruit inflammatory cells Signup and view all the answers

In which condition might streptococcal cell wall antigens contribute to nephritis?

Poststreptococcal glomerulonephritis Signup and view all the answers

What is the primary feature of the Arthus reaction?

Cutaneous vasculitis Signup and view all the answers

What cell types are primarily involved in delayed-type hypersensitivity (DTH) reactions?

CD4+ T cells and macrophages Signup and view all the answers

What cytokine does TH17 primarily produce to amplify its response?

IL-21 Signup and view all the answers

What is a key characteristic of the pathogenesis of systemic immune complex disease?

Formation of immune complexes from soluble antigens Signup and view all the answers

Which statement accurately describes the fate of activated B lymphocytes?

They can differentiate into both plasma cells and memory cells. Signup and view all the answers

How do helper T cells assist B lymphocytes during the immune response?

By expressing CD40L and producing cytokines. Signup and view all the answers

Which types of antigens primarily stimulate the secretion of IgM antibodies?

Polysaccharide and lipid antigens without T cell help. Signup and view all the answers

What role do adjuvants play in the immune response?

They enhance the innate immune response when given with antigens. Signup and view all the answers

Which cell type is primarily responsible for inducing isotype switching in B lymphocytes?

Follicular helper T cells (TFH). Signup and view all the answers

What is the primary function of IgG antibodies?

To opsonize microbes for phagocytosis. Signup and view all the answers

Which characteristic is true about T-dependent antibody responses?

They usually involve complex proteins as antigens. Signup and view all the answers

What is indicated by the term 'affinity maturation' in the context of B cell activation?

The enhancement of antibody binding to antigens. Signup and view all the answers

What role do costimulatory molecules play in T cell activation?

They signal T cells to proliferate and differentiate. Signup and view all the answers

Which of the following best describes the primary mechanism of antigen recognition by B cells?

B cells utilize their membrane-bound antibody receptors to bind antigens. Signup and view all the answers

What is the primary role of CD8+ cytotoxic T lymphocytes?

Killing cells that express foreign antigens Signup and view all the answers

Which immunoglobulin is primarily responsible for neutralizing microbes in mucus membranes?

IgA Signup and view all the answers

What characterizes memory cells in the immune response?

They are antigen-specific and can survive for years Signup and view all the answers

What is the main cause of hypersensitivity reactions?

An imbalance between immune responses and control mechanisms Signup and view all the answers

Which cytokine profile is associated with the production of IgE and activation of eosinophils?

TH2 cytokines Signup and view all the answers

Which type of immunity is conferred to neonates via maternal antibodies?

Passive immunity Signup and view all the answers

What is the role of Toll-like receptors in the innate immune system?

To recognize microbial molecules and damaged cells Signup and view all the answers

What distinguishes autoimmune diseases from allergies?

Autoimmune diseases target self or autologous antigens Signup and view all the answers

What happens to the majority of effector lymphocytes after the elimination of microbes?

They undergo apoptosis Signup and view all the answers

Which type of antibodies can activate the classical pathway of the complement system?

IgG and IgM Signup and view all the answers

Study Notes

Functions of Helper T Cells

Helper T cells mediate immune responses through CD40L and cytokines.
Cytokines produced rapidly in innate immunity respond to microbes via macrophages, dendritic cells, and NK cells.
CD4+ helper T cells express CD40L upon recognizing antigens, activating macrophages and B cells.
Key cytokines include TNF, IL-1, IL-12, and type I IFNs, involved in inducing inflammation and inhibiting virus replication.
Activated CD4+ cells differentiate into effector cells, secreting various cytokines (IL-2, IL-4, IL-5, IL-17, IFN-γ).
TH1 cells produce IFN-γ, which activates macrophages and supports the destruction of ingested microbes through classical activation.
TH2 cells secrete IL-4 and IL-5, which stimulate B cells and activate eosinophils to target helminthic parasites.
TH17 cells release IL-17, recruiting neutrophils and monocytes to combat extracellular bacteria and fungi.

Adaptive Immune Response

Steps: antigen recognition, lymphocyte activation and proliferation into effector/memory cells, antigen elimination, and memory cell persistence.
B lymphocytes become plasma cells after activation, secreting various classes of antibodies.
T-dependent responses require helper T cell assistance to activate B cells via CD40L and cytokine signaling.
Plasma cells can produce different antibody classes: IgM, IgG, IgA, and IgE after isotype switching, influenced by cytokines.

Antigen Presentation and Recognition

Dendritic cells capture and present protein antigens to T cells via class II MHC in lymph nodes.
B cells recognize diverse antigens through membrane-bound antibody receptors, engaging multiple epitopes for activation.
Adjuvants enhance immune response by stimulating innate immunity and promoting the activation of T cells and APCs.

Role of Antibodies

IgG: opsonizes microbes for phagocytosis and provides passive immunity to neonates, with a half-life of about 3 weeks.
IgM: primarily involved in the early immune response, activates the classical complement pathway.
IgA: found in mucosal secretions, neutralizes pathogens in the respiratory and gastrointestinal tracts.
IgE: binds to allergens and activates eosinophils to target parasites.

Hypersensitivity

Hypersensitivity refers to injurious immune reactions that lead to tissue damage or disease.
Reactions can be caused by environmental antigens (allergies) or self-antigens (autoimmune diseases).
Four types of hypersensitivity classifications:
- Type I (immediate): mediated by TH2 cells, IgE, and mast cells.
- Type II (antibody-mediated): involves IgG and IgM antibodies causing cell injury.
- Type III (immune-complex mediated): involves circulating immune complexes inducing inflammation.
- Type IV (T cell-mediated): includes delayed-type hypersensitivity reactions mediated by CD4+ T cells.

Stages of Immune Complex Disease

Immune complexes form when antibodies react with antigens in circulation, leading to various pathogenic responses.
Examples of immune complex-mediated diseases include Systemic Lupus Erythematosus (SLE), Poststreptococcal glomerulonephritis, and Serum sickness.
Acute serum sickness can occur after the administration of foreign proteins, resulting in a systemic immune response that targets these proteins.

Mechanisms of Tissue Injury

Mechanisms causing tissue injury in hypersensitivity involve inflammation, immune complex deposition, and antibody-mediated cytotoxicity.
T cells facilitate inflammatory reactions through cytokine release, recruiting leukocytes that amplify tissue damage.
Chronic inflammation can lead to granuloma formation in response to persistent antigens.

Immunologic Memory

Following an immune response, effector lymphocytes undergo apoptosis while memory cells remain long-lived, providing rapid responses upon re-exposure to antigens.
Memory cells enable quicker and more effective immune responses compared to naïve cells, essential for vaccination strategies.

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Description

Explore the crucial roles of helper T cells in the immune system through their interactions with CD40L and cytokines. This quiz delves into how these cells respond rapidly to microbes and other stimuli, highlighting their importance in both innate and adaptive immunity.