B cell-T helper cell interaction and associated antibody production: Step wise explanation

Humoral immunity: Pathway 2 B cell as antigen presenting cell (APC)
Definition: Humoral immune response refers to the host defense mechanisms that are mediated by antibodies produced by plasma cells of B cells.
It protects against extracellular bacteria and foreign macromolecules.
There are two pathways in antibody production
Pathway 1: B Cell Mediated Pathway which is independent of T helper cells.
We have already discussed this pathway in the last post.
Pathway 2: B Cell- T helper Cell Mediated Pathway
In this pathway, B cell acts as antigen presenting cell


Step 1:
B cell activation=Antigen binding to Naïve B cell receptor.
Antigen degradation inside B cell
B cell possesses B cell receptor or BCR with a single specificity. A naive B cell is the one which hasn't encountered an antigen before. When an epitope of an antigen binds to the B cell receptor, that particular B cell gets activated.
Step 2:
B cell as antigen presenting cells (APCs)

In this pathway, B cells acts as antigen presenting cell that is presenting antigen to T helper cells.

MHC class II receptor is present on all antigen presenting cells like B cells, macrophages, dendritic cells etc.

The antigen is processed inside B cell and is presented on MHC class II to T cell receptor of T helper cell. This MHC class II bound antigenic peptide binds to TCR. T helper cells secrete chemokines or chemical messengers which in turn activates B cells more effectively. T helper cell mediated B cell activation is more effective than independent B cell activation.


Step 3:

Clonal selection and Differentiation:
Division of that activated B cell
This activated B cell is selected to divide forming many copies of that cell. That particular clone of B cell is selected to divide and is called as clonal selection.
Differentiation: Plasma cells and memory B cells
Later this B cells differentiate to form plasma cells or effecter cells and memory B cells
Step 4:
Plasma cells produce antibodies that bind to the antigen and ensure its clearance from the system by agglutination, precipitation or neutralization.
Memory B cells are meant for immunologic memory or secondary immune response. When the same antigen comes for the second time, these memory B cells will recognize it quickly and induce a heightened immune response. This will clear out the pathogen from the system soon.