Protection Against Disease Antibody Mediated Immunity- B cells

Learning Objectives Explain how B lymphocytes are responsible for antibody mediated immunity Describe and explain the role of antibodys in the specific immune response

Starter Crossword

B Lymphocyte formation B lymphocytes are derived from stems cell in the bone marrow (as are t cells) and they undergo further differentiation in the liver, spleen or lymph nodes The plasma membrane of each B cell has protein molecules that are specific for a particular antigen These proteins are called antibodies and are released into the lymph Each B cell has a single antibody type that it is able to make and there are over different types that can be made

Competence When the antibody matches an antigen the B cell is said to be competent After infection a macrophage with an antigen embedded in its membrane causes a competent helper T cell to interact with the appropriate competent B cell The increased activity in lymph nodes during times of infection results in the characteristic swelling of lymphatic tissue near the site of infection A viral or bacterial infection of the upper pharynx often results in swollen tonsils because the lymph nodes in the tonsils are where the B cells are producing antibodies

Antibodies When the antigen is detected the B cell divides repeatedly by mitosis to form a clone and because they are all identical, the plasma cells synthesise large quantities of antibodies of the same kind = clonal proliferation These plasma cells only live a few days but secrete 2000 antibody molecules/second It takes a few days for enough B cells to be made to make enough antibody for it to be detectable in the blood therefore you may feel ill because in the meanwhile the pathogen is reproducing Antibodies eventually get the upperhand though and the symptoms of the illness subside. This is the primary response

Immunity If the antigen invades again a faster response occurs when more antibody is made faster. This is because some of the cells which didn’t divide by mitosis to form the clone form memory cells and remain in the body and can secrete antibody for a long time after= immunity The immune response is stimulated in the body by a particular antigens which are foreign substances A division of labour is caused by the development fo 2 types of lymphocytes T and B

Summary An antigen is detected by a B cell The specific B cell will now clone itself by mitosis The plasma cells secrete specific antibodies and form antibody – antigen complexes Antibodies kill the pathogen by; Preventing pathogens attaching to cells Changing the shape of toxin proteins The memory cells continue to secrete small amounts of antibodies for decades

Tasks Complete the flow chart to show how antibody mediated immunity occurs On the back of the flow chart describe and explain the function of the plasma and memory B cells Complete the past paper questions and then pass to the group opposite to mark Take the mark scheme and check the marking of the group Extension – page 74 application

Primary and Secondary Response

Plenary Quick Quiz 1. What stimulates the immune response by B and T cells? 2. How do cytotoxic T cells destroy pathogens? 3. What is the role of memory B cells in immunity? 4. How do antibodies destroy pathogens?

Homework Hand in BYB7 and BYB678 papers Hand in essays Homework for Wed next week BYB7 paper June 2004 BYB6,7,8 June 2004 The energy essay- use mark scheme to help you write the essay