Question

Daniel: Susan and Joe had a wonderful little boy named Daniel, but he had been having an awful lot of bacterial infections and he was barely a year old. It seemed that the antibiotics cleared up one bacterial respiratory infection only to have another follow shortly. The scary thing was that Daniel had just fought off a case of pneumonia caused by Pneumocystis carnii, a fungal infection that was usually found in people with HIV. Waiting for the test results of an HIV test for their little boy was one of the worst experiences ever. Thank goodness it came back negative. However, it seemed that their troubles were just beginning. After this last lung infection, the fungal one, and a negative HIV test, their doctor had ordered a number of other blood tests, including a genetic test that Susan didn’t fully understand. Apparently the doctor was worried about Daniel’s immune system functions. Susan had also met with a genetic counselor who collected a family history of any immune disorders. The details were vague, but Susan’s mother, Helen, knew that one of her three brothers had died young from an unexplained lung infection. Unfortunately, Grandma Ruth had passed away a few years ago, leaving them with numerous unanswered questions. Susan and Joe had an appointment with their doctor that afternoon to go over the results. When they arrived Dr. Dresdner led them into an office where Ms. Henchey, the genetic counselor, waited. This can’t be good, thought Susan. The doctor began by explaining that they had analyzed Daniel’s blood and found that while he had normal levels of B cells and T cells, his antibody levels were anything but normal. The levels of IgG, IgA, and IgE were very low, almost undetectable, and Daniel had abnormally high levels of IgM and IgD. It appears that his immune system failed to undergo immunoglobulin isotype switching due to a CD40 ligand mutation in Daniel's DNA. Diagram an antibody response graph for a normal 1st and 2nd exposure with the antibodies correctly labeled for each exposure. Then diagram what Daniel's graph would look like, based on his situation. Diagram and/or explain why IgG is low and what CD40's role is? Why is a mutation in that gene a problem? (There is no specific diagram I am looking for here, either diagram it or explain it, depending on which you prefer.)

Answer 1

Immunoglobulin isotype switching

There are five different antibody isotypes in placental mammals including humans.

They are ; IgA,IgM,IgD ,IgE and IgG.

These are antibody isotypes of B cells.

In the Ig represent immunoglobulin.

When an antigen exposes to immature B cell it undergoes maturation and it starts express IgM and IgD.They are membrane bound forms of antibody isotype.The activated B cells bind to antigen.Which encounters specific signalling molecules and start antibody class switching to produce IgA ,IgE,IgG from IgM and IgD.

If this biological system fails to proceeds then it cause high concentration of IgM and IgD antibody isotypes.

High levels of IgM and IgD occurs in X-linked immunodeficiency. It is one of the rare form of primary immunodeficiency disease caused by mutation in the gene that codes for ligand CD40.CD40 ligand is expressed on activated T lymphocytes is required for T cell and B cell to undergo immunoglobulin class switching from IgD to IgE and IgG and IgA.

In immune disorder there will be recurrent infections.

Immunoglobulins cause enhanced phagocytosis , neutralization of toxins, complement mediated lysis and virus neutralization.