Question

Disorders of the immune system – Know the type 1, type 2, type 3, and type 4 hypersensitivity reactions – what are their characteristics, type of Ab involved, type of cells involved, is complement involved? How can they be controlled? Know the ABO and Rh blood systems, hemolytic disease of the newborn.

Disorders of the immune system – immune deficiencies (Bruton’s agammaglobulinemia, DiGeorge syndrome, SCID) and HIV/AIDS. How does HIV actually cause AIDS? Give four different mechanisms which could account for the lowered number of T-helper cells. What are the problems associated with developing an HIV vaccine.

What are autografts, allografts, xenografts? What is the most common transplant? What is recognized as foreign when a tissue is rejected? Which of the immune cells is most important in the rejection process? How do we attempt to make the transplant successful? What drugs are given to suppress the immune response?

Answer 1

ABO blood groups are the most basic system of blood typing. This system divides blood into four groups – A, B, AB and O. The other main grouping used is the Rhesus (Rh) system, which is either negative or positive. Our blood group is a combination of the ABO system and the Rh system: for example, AB positive, A negative etc. Blood group is determined on the basis of antigens present for example in blood group A, A antigen is present, In B, B antigen is present in blood group AB both A and B are present and in blood group O no antigen is present and hence it is considered universal donor blood group unlike AB which has both the antigens and hence it is  considered as universal acceptor blood group.

Bruton agammaglobulinemia or X-linked agammaglobulinemia (XLA) is an inherited immunodeficiency disorder characterized by the absence of mature B cells, resulting in severe antibody deficiency and recurrent infections.

DiGeorge syndrome, also known as 22q11.2 deletion syndrome, is a syndrome caused by the deletion of a small segment of chromosome 22. Symptoms include congenital heart problems, specific facial features, frequent infections, developmental delay, learning problems and cleft palate.

Acquired immunodeficiency syndrome (AIDS) is a chronic, potentially life-threatening condition caused by the human immunodeficiency virus (HIV). By damaging the immune system, HIV interferes with the body's ability to fight the organisms that cause disease. People die with minor infections because of the lack of complete immunity.

HIV attacks a specific type of immune system cell in the body. It's known as the CD4 helper cell or T cell. When HIV destroys this cell, it becomes harder for the body to fight off other infections. HIV destroys CD4 cells by using their replication machinery to create new copies of the virus.

Challenges in developing AIDS vaccine-

HIV continuously mutates and recombination occurs in it frequently than any other viruses.

HIV infects helper T cells so the vaccine is difficult to target it as the vaccine itself depend on the stimulation of Helper T cells.

Lacks a good animal model for vaccine testing. Inability to make antigens that mimic the conformation of the natural epitope.

autograft- transplantation from one part of the body to the other.

allograft- transplantation between different members of the same species for example between two individuals of different families.

Xenograft- transplantation between different members of different species. for example pig to humans

The antigens responsible for such rejection are those of the major histocompatibility antigen (HLA ) system. Rejection is a process in which both cell-mediated immunity and circulating antibodies play a role. Recognition of transplanted cells that are self or foreign is determined by polymorphic genes that are inherited from both parents and are expressed co-dominantly.   

Transplant recipients usually need to take an array of medications. One is immunosuppression. Common approaches include avoidance of steroids, reduced exposure to calcineurin inhibitors, and other means of weaning drugs based on patient outcome and function.

The drugs currently used to suppress the immune system can be divided into three categories:

first, powerful anti-inflammatory drugs of the corticosteroid family such as prednisone; second, cytotoxic drugs such as azathioprine and cyclophosphamide; and third, fungal and bacterial derivatives, such as cyclosporin A