Immunology- Pt 2

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Questions and Answers

Which type of T cells can only recognize antigens presented on MHC1 molecules?

CD4

CD8 (correct)

CD2

CD1

Where are naïve T cells typically located?

Lymph nodes (correct)

Tissue

Cardiac tissue

Bloodstream

Which cell types express MHC2 molecules?

Every nucleated cell

Dendritic cells, macrophages, and B cells (correct)

T cells, B cells, and macrophages

Every unnucleated cell

What happens to the peptides broken down from proteins in the cytosol?

They are presented on the cell surface Signup and view all the answers

What is the role of CD4+ T cells?

To help other immune cells respond to antigens Signup and view all the answers

What is the outcome of the activation of naïve T cells?

Proliferation and differentiation Signup and view all the answers

Which cell type is responsible for activating naïve T cells?

Dendritic cells Signup and view all the answers

What is the role of effector T cells?

To recognize antigens from any cells Signup and view all the answers

What is the primary function of CD4+ Th1 cells?

To activate macrophages and CTLs Signup and view all the answers

What is the primary difference between apoptosis and lysis?

Apoptosis prevents inflammation, while lysis allows it Signup and view all the answers

Which type of immune response is characterized by the production of IgM and the absence of memory cells?

T-independent activation Signup and view all the answers

What is the primary function of CD8+ CTLs?

To kill infected target cells Signup and view all the answers

What is the primary function of B cells in the humoral response?

To recognize antigens directly and present them to T cells Signup and view all the answers

Which type of T cell is involved in the activation of macrophages and CTLs?

CD4+ Th1 cells Signup and view all the answers

What is the primary characteristic of B cell T-independent activation?

It involves the production of IgM and the absence of memory cells Signup and view all the answers

What is the primary function of IgA in the human body?

Providing mucosal immunity and neutralizing microbes and toxins within the GI and respiratory tract Signup and view all the answers

Which of the following have these traits: Thy have their isotype-switched, high-affinity antibodies, memory B cells, and long-lived plasma cells?

T-dependent activation Signup and view all the answers

What is the primary function of IgE in the human body?

Mediating defense against helminths through eosinophil and mast cell activation Signup and view all the answers

What is the primary antibody isotype produced during primary immune responses?

IgM Signup and view all the answers

Which of the following is NOT a function of IgG ?

Mucosal immunity Signup and view all the answers

Where is IgG found?

Blood and tissues Signup and view all the answers

Which of the following statements is correct?

T cells require antigen presentation Signup and view all the answers

Study Notes

Antigen Receptors (T cells and B cells)

T cells require antigen presentation, whereas B cells can approach antigens directly.

Antigen Processing and Presentation (T cells)

The MHC (major histocompatibility complex) molecule has two classes: MHC1 and MHC2.

Class 1 MHC

CD8 (cytotoxic T cells) can only recognize antigens presented on MHC1 molecules.
Every nucleated cell has a class 1 MHC molecule.
MHC1 takes proteins produced in the cells, breaks them down into peptides, and displays them on the cell surface.

Class 2 MHC

CD4 (helper T cells) can only recognize antigens presented on MHC2 molecules.
MHC2 expressing cell types include dendritic cells, macrophages, and B cells.

Naïve T Cell: Activation

Naïve T cells are fully mature T cells that have not yet interacted with antigens.
They are located within lymph nodes.
The activation of naïve T cells is always done by dendritic cells.
Activation involves proliferation and differentiation into effector and memory T cells.

Naïve T cell: Activation Steps

Step 1: Immature dendritic cells encounter antigens in the tissue.
Step 2: Migration to lymphoid tissue and maturation.
Step 3: Antigen presentation by mature dendritic cells in the lymph nodes.

T Cell Subsets (CD4 and CD8)

CD4 is known as the helper T cell, involved in the activation of macrophages, B cells, and other cells.
CD4 has subsets/types: Th1, Th2, Th17.
CD4+ Th1 cells are involved in cytokine secretion, activation of macrophages, and activation of CTLs (CD8+).
CD4 expresses surface molecules and secretes cytokines that activate other cells.

CD8

CD8 is known as the cytotoxic T cell, involved in the killing of infected "target cells" and macrophage activation.
CD8 has a subset/type: CTLs (cytotoxic T lymphocytes).
CD8+ CTLs will only kill pathogens and will never produce cytokines.
CD8+ CTLs induce apoptosis of infected cells.

Apoptosis and Lysis

Apoptosis is when a cell dies without rupturing the cell membrane, preventing inflammation.
Lysis allows the pathogen to leave the cell due to the rupturing of the cell membrane, causing inflammation.

Adaptive Immunity: Humoral Response (B cells)

B cells recognize antigens directly and present them to T cells.
Antigen recognition is not restricted by MHC presentation.

B cell T-independent activation

The production of IgM is the only possible response with T-independent activation.
T-independent activation does not produce memory cells.
T-independent activation B cells have low-affinity antibodies and short-lived plasma cells.

B cell activation by Th cells

When T cells activate B cells, they can have responses including antibody secretion, isotype switching, affinity maturation, and memory B cell formation.
B cell activation by Th cells induces a stronger response than T-independent activation.

Humoral responses involve:

Immunoglobulins (Ig)
Ig Isotypes or classes

Ig Isotypes

Ig isotypes have differences in heavy chain structure, monomeric vs polymeric structure, subclasses, serum concentration, half-life, and functions.

Ig Isotype distribution

IgM is mainly found in blood and is the major antibody of primary responses.
IgG is found in blood and tissues and is the major antibody of secondary responses.
IgA is found in mucous membranes.
IgE is found in epithelial tissue.

Ig Isotype functions

IgM activates the classical pathway of complement.
IgA provides mucosal immunity, neutralizing microbes and toxins within the GI and respiratory tract.
IgE is involved in eosinophil and mast cell mediated defense against helminths.
IgG neutralizes microbes and toxins, provides feedback inhibition of B cell activation, neonatal immunity, antibody-dependent cellular cytotoxicity mediated by NK cells, and opsonization of antigens for phagocytosis by macrophages and neutrophils.

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Description

This quiz covers the difference between T cells and B cells in terms of antigen presentation, MHC molecules, and antigen processing. It also discusses the role of Class 1 MHC and CD8 cells.