B cells are cells that are produced matured in the bone marrow. Each B cell has a different antibody which will only attach to a specific antigen. There are five different classes of antibodies (IgG, IgM, IgA, IgE and IgD), all of which have a different roll. Antibodies are Y-shaped proteins that contains heavy and light chains of proteins. The light chain is situated on the inside of the 'y' and the heavy chain is on the outside. Each antibody have these heavy and light chains but have different variable regions (antigen-binding sites) that distinguishes one B cell from another. After a T-helper cell has identified a foreign molecule, cytokines are secreted which will only react with and bind to a B cell's specific antibody at the antigen-antibody complex. This causes the release of antibodies and B cells to divide, a process also known as clonal selection and expansion and then differentiate into B plasma and B memory cells. as shown in the image below:
As shown in the image above; after having multiplied and differentiated; the B plasma cells produce and secrete large amounts of antibodies which will circulate into the blood stream and bind to the specific antigen according to the specific antibody. The differentiated B memory cells are long lasting in the body, know what you look like and will only respond to their specific antigen. Due to this; the immune system will be ready for the second encounter and ready to carry out the same response of the same pathogen attempts to attack the body again. This second response is faster in comparison to the first encounter with the pathogen due to the presence of B and T memory cells.