Immunology Overview on APCs and MHC

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Questions and Answers

What is the primary function of cytotoxic T cells?

To enhance the function of B lymphocytes

To secrete antibodies against pathogens

To trigger apoptosis in target cells (correct)

To produce memory cells for future immunity

Which characteristic is specifically associated with cytotoxic T cells?

Round nucleus with basophilic cytoplasm (correct)

Secretion of interleukins

Presence of CD4 coreceptors

Production of immunoglobulins

What triggers the activation of cytotoxic T cells?

Antigen presentation by APCs (correct)

Direct interaction with pathogens

Stimulation by B cells

Presence of antibodies in circulation

What type of cells do cytotoxic T cells primarily target?

Virus-infected and malignant cells Signup and view all the answers

What is the significance of perforins released by cytotoxic T cells?

They create pores in target cell membranes Signup and view all the answers

What characteristic distinguishes the large granular lymphocytes described in the content?

They directly lyse unhealthy host cells without an immune response. Signup and view all the answers

Which function is NOT associated with the light region of the germinal center?

Presence of mature lymphocytes ready for activation. Signup and view all the answers

How do the lymphocytes in the dark region of the secondary lymphoid nodules differ from those in the light region?

They mostly consist of smaller and mature lymphocytes. Signup and view all the answers

What type of cells does the dark region contain within the cellular framework of stellate cells?

Smaller and more mature lymphocytes. Signup and view all the answers

What distinguishing feature relates to the cell types that are killed directly by large granular lymphocytes?

They include unhealthy host cells infected with viruses or bacteria. Signup and view all the answers

What is the primary role of Helper T cells in the immune response?

MHC-II mediated recognition of altered cells Signup and view all the answers

Which of the following statements is true regarding immune response and graft viability?

HLA matching is crucial for the success of organ transplants. Signup and view all the answers

In the context of lymphocyte types, which statement best describes Natural Killer (NK) cells?

They play a role in both innate and adaptive immunity. Signup and view all the answers

What does the term 'MHC-II restricted' imply about Helper T cells?

They specifically recognize peptide antigens presented by MHC-II. Signup and view all the answers

Which loci are primarily typed for determining HLA compatibility in organ transplantation?

HLA-A, -B, and -DR Signup and view all the answers

Which cells are primarily responsible for presenting antigens to activate T cells?

Antigen-presenting cells Signup and view all the answers

What is the CD4 normal count range for healthy adults and teens?

500 to 1,600 cells per cubic millimeter Signup and view all the answers

What condition is indicated by a CD4 count of less than 200?

AIDS Signup and view all the answers

The Major Histocompatibility Complex (MHC) is located on which chromosome?

Chromosome 6 Signup and view all the answers

Which type of macrophages are known as Kupffer cells?

Liver macrophages Signup and view all the answers

Which type of T cells are restricted by MHC-I molecules?

CD8 + T cells Signup and view all the answers

What is the primary role of the Major Histocompatibility Complex (MHC) on antigen-presenting cells?

Bind and present peptide fragments to T cells Signup and view all the answers

What type of cells primarily make up the mononuclear phagocytic system?

Monocytes and tissue macrophages Signup and view all the answers

What is the outcome of positive selection for T cells in the thymic cortex?

Only T cells with functional TCRs that recognize MHC class I and II survive. Signup and view all the answers

What percentage of T-lymphocytes make it through the selection process to become functional?

2% Signup and view all the answers

Where does negative selection primarily occur in the thymus?

Thymic medulla Signup and view all the answers

What is the primary function of the cytoreticulum in the thymus?

To support T lymphocytes and other immune cells Signup and view all the answers

What characterizes the progression of pre-T lymphocytes during maturation?

They begin in the cortex and end in the medulla over about two weeks. Signup and view all the answers

What is the role of the Hassall's corpuscles found in the thymic medulla?

To aggregate TECs for later degeneration. Signup and view all the answers

What happens to T-cells that strongly bind self-antigens presented by dendritic cells?

They are eliminated during negative selection. Signup and view all the answers

What can result from the loss of thymus functionality?

Loss of T-cell-mediated immunity. Signup and view all the answers

Study Notes

Antigen-Presenting Cells

Antigen-presenting cells (APCs) phagocytose and process antigens, presenting them to T cells for activation.
Normal CD4 count for healthy adults and teens ranges from 500 to 1,600 cells/mm³.
A CD4 count below 200 indicates susceptibility to infections, including AIDS.

Major Histocompatibility Complex (MHC)

Most APCs belong to the mononuclear phagocytic system.
MHC genes are located on the short arm of chromosome 6 (6pQ).
Specialized integral membrane proteins, MHC-I binds to cytotoxic T cells (CD8) while MHC-II binds to helper T cells (CD4).

Lymphocytes

Lymphocytes include T cells and B cells and are critical constituents of lymphatic tissue.
Cytotoxic T cells destroy virus-infected, foreign, or malignant cells by releasing perforins that trigger apoptosis.
Helper T cells (CD4) are facilitated by MHC-II in activating immune responses.

Immune Response and HLA Matching

Immune response is a determinant of graft viability; HLA typing is crucial for organ transplants in renal, lung, cardiac, and pancreatic cases.
Loci involved in HLA typing are HLA-A, -B, and -DR.

Natural Killer (NK) Cells

NK cells are large granular lymphocytes that play roles in innate and adaptive immunity.
They destroy unhealthy host cells including those infected with viruses or bacteria, and potentially tumorigenic cells, without needing prior sensitization.

Structure of Secondary Lymphoid Nodules

Secondary nodules consist of a dark region (mantle/marginal zone) and a light region (germinal center).
The dark area contains mature lymphocytes with condensed chromatin while the lighter area includes less mature lymphocytes undergoing division.

Thymus and T-Cell Maturation

The thymus has a corticomedullary barrier and supports the maturation of T cells.
Thymocytes undergo a stringent selection process ensuring a functional T-cell receptor (TCR) that does not bind self-antigens strongly.
Positive selection occurs in the cortex allowing T cells that recognize MHC molecules to survive, while negative selection in the medulla eliminates T cells that bind self-antigens.

Thymus Cell Types and Functions

Thymic epithelial cells (TECs) provide structural support and express organ-specific proteins.
Hassall's corpuscles are aggregates of TECs found in the medulla, significant in T cell selection.

T-Cell Mediated Immunity

Only about 2% of T lymphocytes produced will mature and populate secondary lymphoid organs, representing a significant selection process to maintain immune tolerance and functionality.

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Description

This quiz covers fundamental concepts related to antigen-presenting cells (APCs) and the major histocompatibility complex (MHC). Understand the roles of lymphocytes in the immune response, including CD4 and CD8 T cells. Additionally, explore the importance of HLA matching in graft viability.