B lymphocytes and role in specific immune response

humoral immunity

• blood = humor

• antibodies are released into blood lymph

how do b lymphocytes respond

• B lymphocytes respond to antigens found outside the organisms cells eg:

  • on surface of bacteria

  • on surface of fungi

  • soluble antigens eg toxins from bacteria + toxins from snake venom

clonal selection of b lymphocytes

• the antibody receptors on b lymphocytes bind to specific antigens (complementary binding)

• interleukins from helper t cells are also required to activate the B cell

clonal expansion of B cells

• B cells divide rapidly by mitosis to from cones

what do B cell differentiate into

• plasma cells

• B memory cells

plasma cells

• quickly synthesise and secret antibodies

B memory cells

• remain in body for a long time

• reactivate quickly during the secondary response

• giving immunological memory

immunological memory primary response

• antigen presentation, clonal selection and expansion takes time

• infection has time to take hold and we often suffer effects

immunological memory in secondary response

• there is a more rapid response with higher concentration of antibody produced

what are the basis of immunological memory

• memory cells

• last for may years often a lifetime

• clonal expansion happens more quickly in the presence of memory cells

immunological memory graph

antibody structure

• 2 long (heavy) and 2 short (light) polypeptide chains held together by disulphide bridges

• constant region

• variable region

• hinge region

constant strucutre

• the same (same amino acid sequence) in every antibody

• enable the antibody to bind to phagocytes + induce phagocytosis

variable region

• different (diff amino acid sequence) in every type of antibody

• ie they are specific

• their shapes are complementary to that of the antigen which they bind to

binge regions

• these allow flexibility to bind / attach to more than one antigen

1 way antibodies work

• agglutination- large antibodies called agglutin’s can cause pathogens to stick together

• they form a group too large to enter a host cell or are less mobile and easier for phagocytes to engulf

2nd way antibodies work

• opsonisation: antibodies called opsonins bind t pathogens + tag them for recognition by phagocytes

what do antibodies act as

• anti toxins

• they bind to toxins produced by pathogens

• the toxins are made harmelss

how can antibodies cause immobilisation

• if they bind to the bacteria flagella

• it can stop the bacterium moving

how can antibodies cause neutralisation

• antibodies cover the pathogen binding sites

• this prevents the pathogen from binding to a host cell (and therfore entering)