Plasma B cells produce antibodies (also called immunoglobulins) that bind to the antigens which makes it easier for phagocytic cells to target and kill them. There are five classes of immunoglobulins:
1. IgG
2. IgM
3.IgA
4. IgE
5. IgD

Function of Plasma B cells

B cells that recognise a primary encounter with a pathogen are called memory B cells. B cells can survive for a very long period of time in the body and as soon as the body encounters the same pathogen again they are able to react immediately against the pathogen. This is the reason why the second encounter is usually stronger and at a faster pace. Certain vaccines also work on this property of B cells. They introduce weakened or dead pathogens so that the body is produce memory B cells and on subsequent encounters the body is able to recognise the pathogen and act fast. 

Function of Memory B cells

- Antigens (foreign substance) stimulate creation of preexisting B cell the antibodies which recognize the antigen. 
- The genes that code for antibodies are limited – so where does the diversity come from? 
- The antibody diversity is accounted from the genetic changes of the B lymphocytes development. 
- Antibodies are coded by DNA segments: V, J and C for the light chains and V, D, J and C for the heavy chains. Because there are so many segments and many versions of these segments are possible, the possibilities for antibodies are significantly large. 
- Additionally, changes occur once a B cell has encourntered an antigen and secrets antibodies. 
- The B cells divide and the antibody gene mutation increases and creates a trial of nucleotides that vary (one amino acid mutations for every cell generation) and this allows for antigen specificity of the antibody to be fine tuned over many cell generations. This antigen-binding affinity increases with the B cell proliferation. 


Diversity of Antibodies and DNA segments

B lymphocytes, which are commonly called B cells, express surface B cell receptors for antigen immunoglobulins.  B cells are further differentiated based on which kinds of antigens they respond to and which type of antibodies they produce. There are two different types of B cells:
1. Plasma B cells
2. Memory B cells

Michigan State University

State University of New York at Buffalo

The common lymphoid progenitor matures into four mature categories of lymphocytes:

- B lymphocytes
- natural killer (NK) cells
- NK-T cells
- T lymphocytes

Common Lymphoid Progenitors

Chaplin, D. D. (2010). Overview of the immune response. Journal of Allergy and Clinical Immunology, 125(2), S3-S23.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2923430/
doi: 10.1016/j.jaci.2009.12.980

Overview of the Immune Response

B Lymphocytes

T lymphocytes, which are commonly called T cells, express T cell receptors (TCRs) on their surface.  These are transmembrane proteins that bind to processed antigens that are presented by antigen presenting cells (ATCs).  
There are three types of T cells, differentiated on the basis of their functions:
1. Cytotoxic T- cells
2. Helper T cells 
3. Regulatory T cells

T Lymphocytes

Natural killer (NK) cells are large mononuclear lymphocytes that target abnormal cells, including virus-infected and cancerous cells, and lack either T cell receptors (TCRs) or surface immunoglobulin (Ig). Abnormal cells do not express the normal major histocompatibility complex (MHC). Normal MHC markers prevent NK cell activation, so abnormal MHC expression by abnormal cells recruits NK cells (signals cell distress). Binding of NK cells on target cells (and detect abnormal MHC levels) also leads to activation. After activation, NK cells can employ several mechanisms for target cell destruction.

(Photo credits in References)

Natural Killer Cells

Natural Killer (NK)-T cells are lymphocytes that share the characteristics of both NK cells and T cells.  

Learn Before

Related

Learn After