True or false. Please give an explanation for better understanding. All of the m

Question

True or false. Please give an explanation for better understanding.

All of the macrophages in an otherwise healthy human are infected with a virus. The virus is able to use the macrophage's enzymes to produce more viral particles, but it does not kill the macrophages. Will the macrophage be able to activate Helper T cells, cytotoxic T cells, or both? Explain your answer. Be sure to include a description of the interactions between viral antigens, MHC molecules and TCRs found on the macrophage and/or T cells in your answer.

Explanation / Answer

Virus infected macrophages will not be considered as '' Activated " macrophages, as they have not internalised the exogenous antigen (that is virus) by phagocyotosis. Rather, they will serve as target cells for cytotoxic T cell activation as will be producing and secreting several signalling molecules such Interferon gamma among others that will activate cytotoxic t cells.

In general. T cells possess the T cell receptor- CD3 complex ( or TCR CD3 ) complex that engages with the MHC molecules on any antigen presenting cell (APC). Activated macrophages are those that internalise an exogenous antigen by phagocytosis and display them in the context of MHC class 2 molecules. Thus, only activated Macrophages display high levels of MHC class 2 molecules and need to phagocytose an antigen before they can display the same. Therefore, virally infected macrophages will not be able to activate helper T cells (or CD4+ T cells) as CD4 positive T cells ''see'' APCs only in the context fo MHC 2 molecules.

Since virally infected macrophages will possess MHC class 1 molecules in abundance ( due to viral infection) they will be able to activate Cytotoxic or CD8+ T cells as these cells ''see'' APCs in the context of MHC 1 molecules. This constitutes the first step where the naive Tc cell is recognised by a ''licensed APC'' ( please note a licensed APC refers to an APC or a target cell that has had prior interaction with a Th1 type cell, specifically, an antigen complexed with MHC type 2 molecule on such a cell. In addition, licensing also requires co stimulatory interaction between CD40 on the APC and CD40 L on the Th1 cell).

The second step constitutes the co stimulatory signal to be transmitted between CD28-B7 interaction on the Cytotoxic T cell precursor and licensed APC.

Lastly, Interleukin 2 production by the precursor Tc cell and its interaction with the high affinity Interleukin 2 receptor on the surface of the the Tc cell will result in proliferation and differentiaiton of the precursor Tc cell into an activated effector Tc cell. (autocrine signalling effect)

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