Humoral Immunity: B Cells & Antibodies

Humoral activation

Part of 3 line of defense

under adaptive immunity

B cells and antibody mediated

B cell recognition

Antigen binds to B cell surface receptors → receptor mediated endocytosis (antigen goes into B cell) → B cell digests and breaks down antigen into fragments that it displays on MHC 2 protein surface → Th (helper T cells) binds to MHC protein and releases interleukins and activates the B cell

B cell Activation

Once Th binds to MHC 2 protein and releases interleukins → activates B cell → activated B cell begins clonal selection → produce clones of B cells with that react to the same antigen

B cell differentiation

Clones are either memory B cells or plasma cells (mostly)

Plasma cells produce antibodies

while memory B cells stick around long term for faster future response

What do the antibodies actually do PLAN

Precipitation, Lysis, agglutination, neutralization

Antibody → precipitation

antibodies clump antigen molecules (not whole cell) → clumps removed by phagocytes

Antibody - lysis(complement fixation)

classical pathway of complement system (antibody binds to antigen → complement binds to antibody → complement cascade → forms MAC (membrane attacking complex) → forms hole in bacteria causing it to burst or lysis

Antibody - Agglutination

antibodies clumps enemy cells → clumped cells are cleared by phagocytes

Antibody → Neutralization

antibody binds to antigen first and covers/masks the active regions so toxins, viruses, etc can enter cell →can’t attach and enter cell

Primary exposure

Immune reaction to first time exposure of an antigen

• slow antibody appearance (3-6 days)

• IgM first → rises → declines → IgG rises

• memory B cells produced

anamnestic response

secondary response → immune response when reexposed to same antigen

• because of memory b cells → plasma cells form within hr → rapid response so antigen has little effect

• IgG levels increase with a little bit of IgM

Active humoral immunity

When B cells encounter antigen and produce specific antibodies

natural active humoral immunity vs artificial active humoral immunity

natural active → natural production of antibodies from disease/infection

artificial active → production of antibodies reacting to vaccine

Passive humoral immunity

B cells arent challenged by antigens → borrowed antibodies from other sources

immunity is temporary, doesn’t trigger memory, and degraded eventually

natural passive humoral immunity vs artificial passive humoral immunity

natural passive - antibodies given to fetus through placenta or to infant through breastmilk

artificial passive - injecting antibodies from another person or animal