Lecture 17 - Effector Mechanisms of Humoral Immunity Flashcards Preview

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What are the effector functions of Abs?

1. neutralize these agents
2. Opsonize them for phragocytosis
3. Sensitize them for Ab-dependent cellular cytotoxicity
4. Activate the complement system


Abs are produced by plasma cells where?

in primary (bone marrow) and secondary (LNs) lymphoid organs


Abs that mediate protective immunity may be derived from what cells?

short or long lived Ab-producing plasma cells


Abs perform effector functions in various tissues distant from what?

their production sites


Many of the effector functions of Abs are mediated by what?

heavy chain constant region (Fc) of Ig molecules
Different Ig heavy chain isotypes serve distinct effector functions


Ab effector functions are triggered only after what?

After Ag binding


Describe vaccine-induced humoral immunity against polio?

Oral attenuated poliovirus/ nuetralization of virus by mucosal IgA Ab


Describe vaccine-induced humoral immunity against tetanus, diphteria?

Toxoids/ neutralization of toxin by systemic IgG Ab


Describe vaccine-induced humoral immunity against Hep A or B?

Recombinant viral envelope proteins/ neutralization of virus by mucosal IgA or systemic IgG Ab


Describe vaccine-induced humoral immunity against pneumococcal pneumonia, haemophilus?

Conjugate vaccines composed of bacterial capsular polysaccharide attached to a carrier protein/ opsonization and phagocytosis mediated by IgM and IgG Abs, directly or secondary to complement activation


Abs against microbes and microbial toxins block what?

The binding of these microbes and toxins to cellular receptors


How do influenza viruses and gram-negative bacteria attack host cells?

Influenza viruses use their envelope hemagglutinin to infect respiratory epithelial cells
Gram-negative bacteria use pili to attach to and infect a variety of host cells


Abs that bind to microbial structures interefere with the ability of the microbes to do what?

interact with cellular receptors by means of steric hindrance and may thus prevent infection


What blocks the spread of microbes from an infected cell to an adjacent uninfected cell?



What inhibits the pathologic effects of toxins?

Antibodies that block the binding of toxins to cells


What antibodies coat microbes and promote their phagocytosis by binding to Fc receptors on phagocytes?



What are the types of Fc receptors?

1. FcγRI - high affinity - phagocytosis, cell activation
2. FcγRII - low - phago, cell act, feedback inhibition
3. FcγRIII - low - Ab-dependent cell-mediated cytotoxicity
4. FceRI - high - cell act


Binding of Fc receptors (FCγRI) on phagocytes to multivalent ab-coated particles leads to what?

phagocytosis and the activation of phagocytes


WHat are the most efficient opsonins for promoting phagocytosis via high affinity FcγRI (CD64)?

IgG1 and IgG3


Signals from what receptors activate the phagocytes to destroy these opsonized microbes?

Fc receptor


Ab of certain IgG subclasses bind to infected host cells and the Fc regions of the bound Ab are recognized by what receptor on NK cells?



NK cells activated by ADCC kill what cells?

Ab-coated cells
ADCC = antibody-dependent cell-mediated cytotoxicity


What cells function together to mediate the killing and expulsion of some helminthic parasites?

IgE, eosinophils, and mast cells


Worms are too large to be engulfed by phagocytes and they are relatively resistant to what?

The microbicidal products of neutrophils and Mo


What can worms be killed by?

A toxic cationic protein, known as the major basic protein, present in the granules of eosinophils


What can cause the degranulation of eosinophils, releasing the basic protein and other eosinophil granule contents that kill the parasites?

IgE that coat helminths can bind to FCeRI on eosinophils causing these events to happen


What consists of serum and cell surface proteins that interact with one another and with other molecules of the immune system in a highly regulated manner to generate products that function to eliminate microbes?

The complement system


What is one of the major effector mechanisms of humoral immunity and is also an important effector mechanism of innate immunity ?

Complement system


What is the complement system activated by?

microbes and by Abs that are attached to microbes and other antigens


Activation of complement involves the seqential proteolysis of what molecules to generate enzyme complexes with proteolytic activity?