Question

7. Both children have pathogenic bacteria (Hemophilus and pneumococci) in their sputum even though their MHC Class II molecules function normally. Is this directly or indirectly due to their MHC class I deficiency? Explain.

8. How is it possible that the children have high antibody titers to some viruses and low titers to others?

9. What is the role of the TAP proteins?How do the TAP proteins relate to this case study?

Answer 1

7. MHC Class I deficiency is also known as Bare lymphocyte syndrome type I,which is a rare autosomal recessive diseases.In this the children might have developed immunodeficiency of pathogenic bacteria in there septum even though their MHC Class II molecules was functioning normally.Strep pneumonia, Staph aureus, H. influenzae, Klebsiella, E. coli, and Pseudomonas are some of the pathogens reported in children. Hemophilus and pneumococci causes respiratory diseases that is  bronchiectasis when the immunity of body is decreased . MHC Class I deficiency leads to low count of CD8 T cells and shows decreased surface expression. NK cells killing activity also decreases which indirectly cannot fight against pathogens and hence the children gets affected.

8. The children have high antibody titers to some viruses and low titers to others because Different viruses response differently to antibiotics. Children will be given many antibodies and vaccine to fight against pathogens during 1 to 7 years age.But here some viruses will loss its virulence after interacting with MHC molecules and moreover the MHC molecues will create antibodies against it so that when the virus will attack again the body can fight naturally.Other viruses might show low antibody titers because the MHC Class I molecules cannot produce much antibodies needed to fight the virus hance falls ill.

9. The role of TAP proteins(TAP1 & TAP2) is to transport the peptides into the ER lumen. These peptides are formed by breaking of Endogenous antigens by  the proteasome. The endogenous antigens are the main agents  of the adaptive antiviral immune response. The MHC Class I molecules present these endogenous proteins to the CD8 T cells for immune reaction.Finally the peptides are transported from ER lumen to the cell surface. TAP proteins actually acts as a delivery machines.

The TAP proteins relate to this case study as these are the key transporter of antigenic peptides which are generated by the MHC Class I molecules on exposure to viruses or pathogens. Any effect or deficiency in MHC Class I will lead to TAP deficiency. In TAP 1& 2 deficiency is due to homozygous mutation which results in premature stop codon and eventually becomes a non functional protein.TAP is very important in peptide loading of HLA class I molecules which then can show anti viral activity.