Specific immune system B-lymphocytes

Big picture Immune system diseases Non specific immunity Disease survival mechanisms Physical & chemical barriers Infectious Disease Inflammatory Transmission Epidemiology Non-specific Cellular response Specific immunity Vaccination Public Health Immunological surveillance B cells T cells Clonal Selection theory Big picture

Learning outcomes Explain the role of lymphocytes, B cells in the immune system Identify The need for immunological memory Apply the Importance of primary and secondary responses

Specific (s) or non-specific (ns) Third line of defence Specific (only acts on particular pathogen) First immunological surveillance occurs to find/ discover pathogen Then clonal selection needs to occur to find the corresponding lymphocyte to combat the pathogen Line of defence Specific (s) or non-specific (ns) Mechanism employed Function 3rd S Antibodies production from B cells from bone marrow Make antibodies (humoral response)and are found in the lymphoid organs (except the thymus) 3rd S Response by T cells from thymus gland Cellular immunity but also with the regulation of the humoral response

B lymphocytes (b cells) Lymphocytes respond specifically to antigens on foreign cells, cells infected by pathogens and toxins released by pathogens. AN ANTIGEN IS A COMPLEX MOLECULE – RECOGNISABLE AS SELF OR FOREIGN/ NON-SELF ANTIGEN TRIGGERS PRODUCTION OF ANTIBODIES ANTIBODY IS A Y-SHAPED MOLECULE WITH A SPECIFIC RECEPTOR (BINDING SITE)

Specific Immunity Antibody-Antigen Interaction Antigen - any agent capable of eliciting an immune response Isolated molecules Molecules on surface of cell or virus * A specific antibody molecule will be able to recognize a specific (epitope ) antigen Antibody binds to antigen

B Cell activation B CELLS PLAY THREE IMPORTANT ROLES IN THE IMMUNE RESPONSE:   THEY PRODUCE ANTIBODIES IN RESPONSE TO SPECIFIC ANTIGENS THEY PERFORM THE ROLE OF ANTIGEN-PRESENTING CELLS THEY DEVELOP INTO MEMORY B CELLS.

B CELL ANTIBODIES EACH B CELL CAN A PRODUCE A SPECIFIC ANTIBODY THAT CAN RECOGNISE A SPECIFIC ANTIGEN FROM A PATHOGEN OR TOXIN. THE ANTIBODY WILL BIND TO THE ANTIGEN, FORMING AN ANTIGEN–ANTIBODY COMPLEX. THE ANTIGEN–ANTIBODY COMPLEX HAS TWO MODES OF ACTION: IT MAY INACTIVATE THE PATHOGEN/TOXIN (NEUTRALISATION), RENDERING IT SUSCEPTIBLE TO PHAGOCYTOSIS. IT MAY STIMULATE A RESPONSE, RESULTING IN CELL LYSIS.

Agglutination Antibodies can cause microbes to stick together This makes it easier for phagocytes to engulf them

Inactivate Antibodies can bind to pathogen Causing them to become inactive / rendering them harmless

Neutralisation Some pathogens make us ill by producing toxins Some antibodies work by neutralising these toxins

Stimulate cell lysis The binding of an antibody to the surface of a pathogen can set of a chain reaction with blood proteins, which... ... causes the pathogen to swell up an burst.

Need a little help from my friends .... B cells can identify specific antigens and present them to T cells. T cells can then destroy the pathogen.

Signal 1 antigen & antigen receptor * T Helper Cells Signal 2 - T cell help Th Th B Y 1. T cell antigen receptor 2. Co-receptor (CD4) Signal 1 antigen & antigen receptor 3.CD40 Ligand

More About T-Lymphocytes Help the humoral response by involvement in the maturation of B cells and by triggering the production of antibodies by B-cells Helper T-cells: B-cell Antigen SIGNAL Helper T-cell

Clonal selection theory The body has a large number of lymphocytes each with a single type of membrane receptor specific for one antigen. When a receptor is activated by the binding of an antigen, the lymphocyte repeatedly divides resulting in a clonal population of lymphocytes. http://www.nature.com/nature/journal/v421/n6921/images/nature01409-f1.2.jpg Cell division

Summary slide Specific defences Immune surveillance A range of white blood cells constantly circulate monitoring the tissues. If tissues become damaged or invaded, cells release cytokines which increase blood flow resulting in specific white blood cells accumulating at the site of infection or tissue damage. Recognition of self and non self through specific surface proteins (antigens) Lymphocytes respond specifically to antigens on foreign cells, cells infected by pathogens and toxins released by pathogens.

Summary slide specific defences B lymphocytes Each B lymphocyte clone produces a specific antibody molecule that will recognise a specific antigen surface molecule on a pathogen or a toxin. Antigen-antibody complexes may inactivate a pathogen or toxin or render it more susceptible to phagocytosis. In other cases the antigen-antibody complex stimulates a response which results in cell lysis. B lymphocytes activated by antigen presenting cells and T lymphocytes produce a clone of B lymphocytes that secrete antibodies into the lymph and blood where they make their way to the infected area.

Summary slide Specific defences Immunological memory cells Some T and B lymphocytes produced in response to antigens by clonal selection survive long term as memory cells. A secondary exposure to the same antigen rapidly gives rise to a new clone of lymphocytes producing a rapid and greater immunological response.