Immunology: Humoral immunity

Question 1

What immunoglobulin do B cells have on their surface?

Answer 1

IgM and IgD

Question 2

What immunoglobulin do plasma cells secrete?

Answer 2

IgG- which has specificity for one epitope only

Question 3

What three signals are required for naive B cell activation?

Answer 3

a) binding of antigen to their surface immunoglobulin (B cell receptor)( IgM / IgD) & internalisation
b) molecular interaction with Th2 cells in T cell areas of lymphoid tissue. CD40-CD40L binding
c) co-stimulation by cytokines from the Th2 cell

Question 4

What does the presence of IgM mean?

Answer 4

Indicates the acute phase of the antibody response

Question 5

On activation, B cells undergo…

Answer 5

Class switch
Clonal proliferation
Transformation into lymphoblasts then plasma cells
Formation of memory cells

Question 6

Where do antigens drain to during an immune response?

Answer 6

During an immune response, antigen drains to the local lymph nodes, where naïve B cells are activated and multiplying plasma cells are found in the germinal centres of the lymph node

Question 7

Where are antibodies produced by plasma cells secreted from?

Answer 7

Antibody can be secreted in lymph node, spleen, or wherever there is lymphoid tissue. Plasma cells tend to remain in lymphoid tissues, rarely found in blood but sometimes in tissues.

Question 8

Where does the antigen bind to the BCR?

Answer 8

At the fab region
This specificity of this region for a particular antigen remains the same as the B lymphocyte transforms into plasma cell.

Question 9

What is the fc region of the BCR responsible for?

Answer 9

WTF
The Fc region is more constant. It’s crucial in determining the biological activity and effector functions which the antibody has when an antigen is bound. The Fc region is responsible for actively transporting immunoglobulin to specific locations. For example IgG across mucosal membranes such as the gut or IgA into mucus. Another example is that the Fc region of antibody can bind complement (promoting opsonisation), the Fc region of IgG can bind to Fc receptors (FcR) on polymorphonuclear leucocytes (neutrophils), macrophages or host tissues. If the antigen – antibody complex is bound to these cells by its FcR, then the complex is phagocytosed and the antigen destroyed – yippee!

Question 10

What does soluble antibody do?

Answer 10

Soluble antibody can bind directly to pathogens or toxins. The effect is the pathogen is neutralized and can’t infect any more host cells

Question 11

What are the five antibody isotopes?

Answer 11

GAMED

Question 12

What determines the class of an antibody (GAMED)?

Answer 12

Its Fc region (the number of carbs on the Fc region)

Question 13

What is IgE responsible for?

Answer 13

Allergic reactions

Question 14

Following exposure to an infectious pathogen or toxin, a primary immune response develops in which the lymphocytes are naïve, what happens to the class of antibody?

Answer 14

The first type of antibodies detected in serum are IgM then class switching occurs so that IgG predominates.

Question 15

Describe the primary immune response?

Answer 15

» short lived
» low magnitude
» isotype is IgM (low affinity), but multiple binding sites mean it’s good at agglutinating pathogens
» initiated in local lymph nodes (Ag presented to naïve lymphocytes)
» memory cells established

Question 16

Describe the secondary immune response?

Answer 16

» more rapid (recall of memory cells)
» longer duration
» higher magnitude
» initiated in local lymphoid tissues (activation of primed lymphocytes)
» isotype switches to predominance of IgG & IgA
» higher affinity for antigen

Question 17

How is the maturation of the immune response from primary to secondary detectable?

Answer 17

The maturation of the immune response is detectable diagnostically as a change in Ab isotype to predominantly IgG and Ab amount as well as affinity after 2nd immunization.
The presence of IgM indicates an acute phase of the Ab response to an antigen / pathogen

Question 18

What happens to the maternal antibodies ingested in the colostrum?

Answer 18

Maternal antibodies in colostrum either remain in gut (IgA) or are simply transferred (IgG; passive transudation or active transport) from the gut lumen, across the gut epithelium into the local blood vessels and extracellular spaces, then spreads systemically

Question 19

How long do the maternal antibodies protect the newborn?

Answer 19

Several months

Question 20

What does colostrum contain?

Answer 20

IgG – transported across the gut epithelium to provide protection in blood and interstitial spaces. Major component
IgA – protects gut epithelium against bacteria invasion until newborn’s own IgA production starts
IgM & IgE
Cytokines (e.g. bovine IFNg, TNFa, IL-6, IL-6b)
Trypsin inhibitors
Lymphocytes, majority T cells, some migrate into maternal blood stream

Question 21

How is IgG transported across the gut epithelium?

Answer 21

IgG transport protein: Fc receptor neonatal (FcRn) expressed on gut epithelium
Two molecules of FcRn bind one molecule of IgG
Binding is via Fc portion of IgG
Endocytosis to reach local capillaries

Question 22

What types of placenta transfer a little bit of passive immunity?

Answer 22

Endotheliochorial placenta (puppy & kitten): IgG 5-10%

Question 23

What types of placenta transfer no passive immunity?

Answer 23

Syndesmochorial (calf, lamb, ruminants)
Epitheliochorial (foal & piglet)
No placental transfer, entirely reliant on colostrum

Question 24

What factors influence the success of passive immunity?

Answer 24

» Infection & vaccination history of mother e.g. efficacy & duration of immunity
» Maternal immune response to vaccines
» Concentration of antibodies in mother’s serum & hence colostrum
» Colostrum lost pre-parturition (mother “runs milk”)
» Number of young
» Teat conformation
» Vigour of offspring e.g. time to standing & suck reflex
» Patency of gut epithelium to antibodies (closes by 12-36h post partum)

Question 25

Name three tests that can determine the level of IgG in a newborn, and thus the success of passive transfer,

Answer 25

1. Turbidity test using precipitation of immunoglobulins
2. Single radial immunodiffusion
3. Latex agglutination

Question 26

How do you use the Turbidity test using precipitation of immunoglobulins to determine passive transfer?

Answer 26

– chemical + serum = precipitate
– quantify using spectrophotometer & standard curve
– e.g. zinc sulphate, glutaraldehyde, sodium sulphite

Question 27

How do you use single radial immunodiffusion to determine the success of passive transfer? pros/cons?

Answer 27

– Agar gel, antiserum to IgG + serum
– have to wait 18-24h for result
– more accurate & specific

Question 28

How do you use latex agglutination to determine the success of passive transfer? Pros/cons?

Answer 28

– latex particles coated with anti-IgG + serum = agglutination
– Takes 10mins
– reliable, rapid

Question 29

What is the recommended colostrum intake?

Answer 29

The recommendation is to give a first feed of 3 litres or 10% of body weight within 2 hours. This should be followed up by another similar size feed within 12 hours of birth.

The efficiency of antibody absorption from colostrum declines rapidly from over 40% at birth to less than 5% by 20 hours.