Lecture: Adaptive Immunity

Flashcards generated from a microbiology lecture transcript focusing on adaptive immunity, T cells, B cells, and antibody function for exam preparation.

What is the function of cytotoxic T cells?

The primary function of cytotoxic T cells is to kill host cells infected with intracellular pathogens.

What is the role of helper T cells in adaptive immunity?

Helper T cells provide a confirmation signal necessary for the activation of cytotoxic T cells and B cells.

Where do T cells mature, and what proportion of lymphocytes do they comprise?

T cells mature in the thymus and constitute approximately 75% of lymphocytes.

What are T cell receptors, and what are their main components?

T cell receptors are found on all T cells and consist of a constant region (similar for T cells of the same type) and a variable region (unique for each T cell with antigen-binding sites).

How do T cells recognize antigens?

T cells require that antigens be presented to them on MHC (major histocompatibility complex) molecules.

What are the differences between MHC class I and MHC class II presentation?

MHC class I presents endogenous antigens and can be presented by any nucleated cell, while MHC class II presents exogenous antigens and can only be presented by professional antigen-presenting cells (B cells, macrophages, dendritic cells).

What occurs when a T cell receptor binds to the MHC antigen complex?

When a T cell receptor binds to the MHC plus antigen, clonal selection of the T cell happens.

What type of MHC do cytotoxic T cells recognize antigen on?

Cytotoxic T cells recognize antigen presented on MHC class I molecules.

Why is it important for cells to present antigen on MHC class I?

MHC class I presence communicates that the cell is infected so cytotoxic T cells can eliminate it.

What type of MHC do helper T cells recognize antigen on?

Helper T cells recognize antigen presented on MHC class II molecules, leading to their activation and the subsequent confirmation signal.

Describe the role of dendritic cells in activating helper T cells.

The dendritic cell presents antigens on MHC class II to travel to the lymph node.

How do dendritic cells initially encounter and process exogenous antigens?

Dendritic cells use toll like receptors to bind a PAMP on some exogenous antigens.

What happens during clonal selection of helper T cells?

Clonal selection happens when the T cell receptor binds to the MHC class 2 antigen, selecting that T Cell to activate.

What are the possible fates of a helper T cell after clonal selection?

After clonal selection, a helper T cell becomes either a TH1 cell (responsible for activating cytotoxic T cells via IL-2) or a TH2 cell (responsible for activating B cells via CD40L).

What function does IL-2 have?

IL-2 is responsible for the activation of cytotoxic T cells

What does a TH2 cell secrete?

TH2 cells make a protein and put it on their surface called CD40L to give a confirmation signal to activate B cells.

What has to happen for cytotoxic T cell activation?

For cytotoxic T cell activation, the T cell receptor has to see an antigen presented to it on MHC class one.

What has to happen for cytotoxic T cells to be fully activated?

For cytotoxic T cells to be fully activated, I l two from that helper T cell has to bind the I l two receptor which causes I l two secretion.

How do cytotoxic T cells kill infected host cells?

Perforin, a poison released by cytotoxic T cells, builds holes in the cell surface. Gramzyme then enters the cell, triggers it to kill itself (apoptosis), causing the cell to implode in itself to not let pathogens spread.

What are the five ways antibodies work?

Antibodies, acting on extracellular pathogens, work by neutralization, agglutination, complement activation, antibody mediated cell dependent cytotoxicity, and oxidization.

What is a B cell receptor?

A B cell receptor is an antibody that's tethered into the membrane of the B cell.