Question

Explain the processes that a “naïve” B cell goes through to become activated.

The picture shows a B cell in one situation at the top, followed by another situation below the arrow.

A complete answer minimally starts with what is happening in the picture, and refers to the cells and molecules shown with clear, specific names. You will also describe in reasonable detail what happens to the B cell once it is activated. What outcomes and what function(s) result?  

Answer 1

B cells are activated when their B cell receptor (BCR) binds to either soluble or membrane bound antigen. This activates the BCR to form microclusters and trigger downstream signalling cascades.Interaction between the BCRs on a naïve mature B cell and a free protein antigen stimulate internalization of the antigen, whereas interaction with antigens associated with an intact pathogen initiates the extraction of the antigen from the pathogen before internalization. Once internalized inside the B cell, the protein antigen is processed and presented with MHC II. The presented antigen is then recognized by helper T cells specific to the same antigen. The TCR T cell receptor)of the helper T cell recognizes the foreign antigen, and the T cell’s CD4 molecule interacts with MHC II on the B cell. Once activated cells produce and secrete cytokines that activate the B cell and cause proliferation of B cell . The B cells that have begun proliferating differentiate into short-lived plasma cells called plasmablasts. They secrete antibody as an early attempt to neutralize the foreign antigen. They do not survive more than three days but the antibody produced can provide important assistance to stop fast-dividing pathogens such as viruses. Memory B cells circulate throughout the body on the lookout for antigen with a high-affinity for their BCR and then quickly respond to the antigen, stopping infection. This is how vaccination works. As your body has been previously exposed to the antigen the immune cells(the memory cells) can quickly respond to remove the antigen if it is encountered again, stopping you getting sick.