The initiation of a humoral immune response involves a complex interaction of the antigen, cells and intercellular messengers. Which of the following statement(s) concerning the initiation of the humoral immune response is/are correct?

a. Helper T lymphocytes stimulate B lymphocytes through secretion of cytokines such as interleukin 4 and 6

b. A number of cells can aid in presenting the antigen to the helper T cell including B lymphocytes and macrophages

 Stimulation of the immune system occurs after a variety of antigen-presenting cells (B lymphocytes, macrophages, dendritic cells, and Langerhans cells) act to engulf, process, and present antigen to T lymphocytes of helper lineage. These T lymphocytes, in turn, act to stimulate B lymphocytes to become mature plasmacytes (through secretion of cytokines such as interleukin 4 and 6) dedicated to the production of antibody directed against the specific antigen. An antigen may be defined as any substance that stimulates the host immune response; that is, that the host immune system recognizes is foreign. Thus, an antigen may be an invading microorganism, an inert particle, or any type of chemical compound that triggers the host immune system. Although some antigens are able to directly stimulate B lymphocytes in and of themselves to produce antibody (many polysaccharides), most antigens require coordinated efforts of the various cellular components of the immune system.