Unit A 17 Phys, Immune System Focus on Mechanism of T Lymphocyte Function

Cancer cells

T lymphocytes defend against body cells with intracellular pathogens such as virus infected cells, and abnormal body cells such as _____________________

- T cells must be in direct contact with their targets hence referred to as cell-mediated immune response.

Thymus gland

T cells are produced in the bone marrow and mature in the ____________, hence their name.

T cell receptors

T cells have ______________________ on their cytoplasmic membrane. Are analogous to BCRs that are antibodies, but TCRs are composed of two polypeptides containing a single epitope-binding site between them.

Variable region

TCRs are composed of two polypeptides containing a single epitope-binding site between them. Each of the polypeptides consists of two domains. The ______________________ domain binds to the antigen and is so named because its amino acid sequence varies between receptors of different T cells. In contrast, the constant region domain has less variation. The differences in the amino acid sequences of the variable region is the molecular basis of the diversity of antigens the receptor can recognize

Same

There are many (~billion) T cells carrying different variations of TCRs, but each T cell has thousands of the _________________ type of TCR on its membrane that binds to the same antigen. This increases the likelihood of binding when an antigen is encountered.

Major histocompatibility complex molecules (MHCs).

T cells cannot recognize and therefore cannot respond to, 'free' antigens. They can only recognize and respond to an antigen that has been processed and presented by cells with the antigen bound to specific molecules called __________________________. Give the name and abbreviation in parentheses.

Proteins

Major histocompatibility complex molecules (MHCs) can also be called major histocompatibility complex _____________

CD8

T cell receptors have a co-receptor known as either CD4 or ____________ depending on the type of T cell. The co-receptor functions to 1) stabilize the TCR with the major histocompatibility complex (MHC) proteins and 2) enhance the activation of the T cell.

Cluster of differentiation

The abbreviation CD at the beginning of CD4 and CD8 stands for___________________________

Helper T cells

CD4 co-receptors are on _____________________ and bind to MHC class II molecules.

MHC class II molecules

CD4 co-receptors are on Helper T cells and bind to _______________________. Give abbreviation and include specific class.

Cytotoxic T cells

CD8 co-receptors are on _____________________ (also called Killer T cells, cytotoxic T lymphocytes or CTLs) and bind to MHC class I molecules.

MHC class I molecules

CD8 co-receptors are on cytotoxic T cells (Killer T cells, cytotoxic T lymphocytes or CTLs) and bind to ______________________. Give abbreviation and include specific class.

Human Leukocyte Antigens (HLAs)

Major Histocompatibiltiy Complex (MHC) molecules, also known as _____________________________ (give name and abbreviation in parentheses), are glycoproteins that are made within each body cell (except red blood cells) and inserted into the cell membrane. They have two major functions: 1) self-antigens, 2) Displays antigen to T cells.

Human Leukocyte Antigens (HLAs)

______________________ (give name and abbreviation in parentheses) is the terminology used to describe the primary tissue antigens that determine whether donated tissue is recognized as foreign by the recipient’s immune system. A tissue graft or transplanted organ is more likely to be successful if donor and recipient share the same HLA antigens

MHC molecules

T cells cannot recognize free antigens. They can only recognize and respond to an antigen that is presented by cells via ____________________. Use abbreviation for answer.

Nucleated

MHC class I molecules are found on all ________________ human cells.

- Are the cell's self-antigens

Viral replication

Cytotoxic T lymphocyte (also called CTLs, Cytotoxic T cells, CD8+ cells) recognize endogenous antigens bound to MHC class I proteins. Examples include:

• Viral proteins produced in virus-infected cells during ________________________

• Proteins produced by intracellular bacteria and parasites.

• Tumor antigens produced by cancer cells

• Processed antigens by antigen presenting cells such as dendritic and macrophages use MHC I molecules to activate cytotoxic T cells.

Cancer cells

Cytotoxic T lymphocyte (also called CTLs, Cytotoxic T cells, CD8+ cells) recognize endogenous antigens bound to MHC class I proteins. Examples include:

• Viral proteins produced in virus-infected cells during viral replication

• Proteins produced by intracellular bacteria and parasites.

• Tumor antigens produced by ________________________

• Processed antigens by antigen presenting cells such as dendritic and macrophages use MHC I molecules to activate cytotoxic T cells.

Antigen presenting cells

Cytotoxic T lymphocyte (also called CTLs, Cytotoxic T cells, CD8+ cells) recognize endogenous antigens bound to MHC class I proteins. Examples include:

• Viral proteins produced in virus-infected cells during viral replication

• Proteins produced by intracellular bacteria and parasites.

• Tumor antigens produced by cancer cells

• Processed antigens by _______________________ such as dendritic and macrophages use MHC I molecules to activate cytotoxic T cells.

Antigen presenting cells

Both MHC class I and MHC class II molecules are found on ________________________ that include macrophages, dendritic cells, and B cells. Extracellular pathogens engulfed, degraded, and placed on both MHC class I and MHC II proteins.

Helper T cells

MHC class II molecules are found primarily on antigen presenting cells (APCs) that include macrophages, dendritic cells, and B cells. Extracellular pathogens engulfed, degraded, and placed on MHC II proteins.

- MHC-II are recognized by _____________ (also called CD4+ cells)

T cells

Antigen-presenting cells (APCs) are specialized cells used to activate __________________. APCs process pathogenic or abnormal cellular particles usually by breaking them into smaller fragments and then presenting the fragments on their cell surfaces using MHC molecules

MHC molecules

Antigen-presenting cells (APCs) are specialized cells used to activate T cells. APCs process pathogenic or abnormal cellular particles usually by breaking them into smaller fragments and then presenting the fragments on their cell surfaces using _________________________. Use abbreviation for answer.

Macrophages

APCs include _________________, dendritic cells, and B cells that use both MHC class I and class II molecules to activate T cells, although B cells present primarily by MHC class II and less by class I.

Dendritic cells

APCs include macrophages, _________________________, and B cells that use both MHC class I and class II molecules to activate T cells, although B cells present primarily by MHC class II and less by class I.

MHC class I molecules

The type of MHC molecule used determines the type of T Cell that is activated.

• _____________________ (use abbreviation and specific class for answer) activate Cytotoxic T Lymphocytes (also called CTLs, Killer T cells, CD8+ cells, cytotoxic T cells).

• MHC class II molecules activate Helper T cells (CD4+ cells).

MHC class II molecules

The type of MHC molecule used determines the type of T Cell that is activated.

• MHC class I molecules activate Cytotoxic T Lymphocytes (also called CTLs, Killer T cells, CD8+ cells, cytotoxic T cells).

• ____________________ (use abbreviation and specific class for answer) activate Helper T cells (CD4+ cells).

Professional

Antigen-presenting cells (APCs) can be classified into two categories: Professional and non-professional.

- _________________________ APCs are the macrophages, dendritic cells, and B cells and can express both MHC class I and class II to activate T cells.

Non-professional

Antigen-presenting cells (APCs) can be classified into two categories: Professional and non-professional.

- _________________________ APCs can only express MHC class I and include the rest of the nucleated body cells. Remember that healthy nucleated cells use MHC I molecules as their self-antigens displaying proteins that are synthesized by the cell so they are not destroyed by cytotoxic T cells. Cells infected with an intracellular pathogen (viral or bacterial) or have become cancerous, will have abnormal proteins (antigens) attached/displayed on their MHC I molecules and activate cytotoxic T cells to kill them.

MHC class I molecules

Non-professional APCs can only express MHC class I and include the rest of the nucleated body cells. Remember that healthy nucleated cells use ______________________________ (use abbreviation and specific class for answer), as their self-antigens displaying proteins that are synthesized by the cell so they are not destroyed by cytotoxic T cells. Cells infected with an intracellular pathogen (viral or bacterial) or have become cancerous, will have abnormal proteins (antigens) attached/displayed on their MHC I molecules and activate cytotoxic T cells to kill them.

Cytotoxic T cells

Cells infected with an intracellular pathogen (viral or bacterial) or have become cancerous, will have abnormal proteins (antigens) attached/displayed on their MHC I molecules and activate _____________________ to kill them.

Helper T cells

Three main types of T cells:

- ____________________

- Cytotoxic (killer) T cells

- Regulatory or suppressor T cells

Antigen presenting cells

Helper T cells are also referred to as CD4+ cells because in addition to their T cell receptor, they also have a co-receptor known as CD4 (cluster of differentiation) that assists in binding to MHC class II molecules of ______________________

MHC class II molecules

Activation of a naive Helper T cell to effector Helper T cells and memory cells requires an antigen presenting cell that presents foreign antigen in combination with ________________________. (Use abbreviation and specific class for answer)

T cell receptors

Once activated, Helper T cell undergoes clonal expansion producing effector cell and memory cell clones with the same _______________

Plasma cells

Helper T cells secrete cytokines that "help" or enhance nearly all aspects of the immune response including:

- Bind to B cells and helps promote their differentiation into antibody producing ______________________ and memory B cells.

- Enhances activity of cytotoxic T cells, regulatory T cells, & even other helper T cells

- Release chemotaxins that attract neutrophils & macrophages and stimulates macrophage activity

Helper T cells

HIV destroys cell known as ______________________, which decreases the body's ability to defend against cancer and pathogens.

MHC class I molecules

Cytotoxic T Lymphocytes (CTLs, Cytotoxic T cells, killer T cells, CD8+ cells) are microscopic "hit men" that destroy host cells bearing foreign/abnormal antigen (e.g., cancer cells and host cells invaded by intracellular pathogens such as viruses) displayed on ________________________. (Use abbreviation and specific class for answer)

Perforin

Cytotoxic T cells kill infected host cells by:

· Releasing _____________________ molecules that penetrate the target cell's surface membrane forming holes or channels and depending on how many holes form, can allow fluid to flow rapidly into the cell and cause it to lyse.

· Releasing granzymes, which are enzymes that enter through the perforin channels and cause the cell to self-destruct through apoptosis.

Granzymes

Cytotoxic T cells kill infected host cells by:

· Releasing perforin molecules that penetrate the target cell's surface membrane forming holes or channels and depending on how many holes form, can allow fluid to flow rapidly into the cell and cause it to lyse.

· Releasing _________________, which are enzymes that enter through the perforin channels and cause the cell to self-destruct through apoptosis.

Apoptosis

Cytotoxic T cells kill infected host cells by:

· Releasing perforin molecules that penetrate the target cell's surface membrane forming holes or channels and depending on how many holes form, can allow fluid to flow rapidly into the cell and cause it to lyse.

· Releasing granzymes, which are enzymes that enter through the perforin channels and cause the cell to self-destruct (cell suicide) through _______________________.

Regulatory T cells

___________________________, also called suppressor T Cells,

• Regulate/suppress plasma cell antibody production & cytotoxic & helper T cell activity; effects are primarily the result of chemicals called CYTOKINES (or LYMPHOKINES)

• Prevents excessive immune response which might be detrimental to body

• May also prevent immune system from attacking a person's own cells & tissues