Question

1. Denote the isotype (if any) of all the maternal antibodies that protect the following locations.
   1. The blood of a fetus
   2. The blood of a newborn
   3. The mucus membranes of a newborn
   4. The mucus membranes of an infant 1 month after birth who is breastfeeding
   5. The mucus membranes of an infant 1 month after birth who is NOT breastfeeding
   6. The blood of an infant 1 month after birth who is breastfeeding
   7. The blood of an infant 1 month after birth who is NOT breastfeeding
   8. The mucus membranes of an infant 1 year after birth who is breastfeeding
   1. The mucus membranes of an infant 1 year after birth who is NOT breastfeeding
   10. The blood of an infant 1 year after birth who is breastfeeding
   11. The blood of an infant 1 year after birth who is NOT breastfeeding

Answer 1

When the constant region of an antibody heavy chain was sequenced, it revealed five types of chains called isotypes, which are designated as µ, δ, γ, ε, α. Accordingly, five types of antibodies are differentiated as, IgM, IgD, IgG, IgE and IgA. Light chains of each class of antibody are either κ or λ type. The basic feature of different classes of antibodies are:

1) Immunoglobulin G (IgG) – they are most abundant antibodies in serum (80%). As per their differences in γ-chain, IgG subclasses are IgG1, IgG2, IgG3, and IgG4. Certain important functions of IgG are: a) IgG1, IgG3, IgG4 can cross placental barrier and help in proting the fetus. b) IgG3, can most effectively activate complement proteins, ad also IgG1 and IgG2 to lesser extent. c) IgG1 and IgG3 help in opsonization process.

2) Immunoglobulin M (IgM)- They constitute 5% to 10% ot total serum antibodies. Five IgM subunits may bind at FC regions to form pentamer by joining (J) chain. In response to antigen, IgM is the first antibody to be produced. IgM is the first antibody secreted in neonates.

3) Immunoglobulin A (IgA)- comprises of 10% to 15% of total serum immunoglobulins. IgA exists as monomers, dimers, trimers, tetramers. Dimers and tetramers of IgA constitute of secretory components along with IgM.

4) Immunoglobulin E (IgE)- comprises of 0.3 microgram per milliliter. IgE mediate hypersensitive reactions causing symptoms like hay fever, hives, asthma, anaphylactic shock or non-allergic reaction like wheal and flare reaction (also called P-K reaction as per Prausnitz and Kustner).

5) Immunoglobulin D (IgD)- constitute 0.2% of serum immunoglobulins. Along with IgM, IgD form membrane receptor of B cells.

Answers:

a. Blood of fetus- IgG. As crosses placenta

b. The blood of a newborn- IgG. Remains in blood for 6 months after birth.

c. The mucus membranes of a newborn- None. Occurs after breast feeding.

d. The mucus membranes of an infant 1 month after birth who is breastfeeding- mainly IgA (also IgG, IgM, IgD, IgE) present in secretion like breast milk.

e. The mucus membranes of an infant 1 month after birth who is NOT breastfeeding. None.

f. The blood of an infant 1 month after birth who is breastfeeding. IgG, IgA. Some IgA obtained through breast milk lines respiratory ad intestinal lining and enter blood of baby.

g. The blood of an infant 1 month after birth who is NOT breastfeeding. IgG

h. The mucus membranes of an infant 1 year after birth who is breastfeeding- None. Maternal antibodies are degraded over time after birth.

i. The mucus membranes of an infant 1 year after birth who is NOT breastfeeding- None. No maternal antibodies.

j. The blood of an infant 1 year after birth who is breastfeeding IgA, supplied from breast milk.

k. The blood of an infant 1 year after birth who is NOT breastfeeding- None. No maternal antibodies.