Question

Victoria and Rusty were worried about their infant Bailey since his first trip to the hospital at 3weeks of age. That time he had a temperature of 103°F and a runny nose. The emergencyphysician checked Bailey over but sent him home saying it was only a common cold, probablybrought home by his older siblings, and that all would be fine. But Bailey's health has not beenfine as he has been having an unusual number of bacterial infections and he is not yet quite 1year old. The antibiotics that Bailey's physician prescribed have cleared up his bacterialrespiratory infections but another infection always follows.Now that Bailey is back at the hospital with pneumonia, his physician has ordered a number ofother laboratory tests as he is now worried about Bailey's immune system. The studies showedthat Bailey had normal levels of B cells and T cells, with his immunoglobulin levels andhematology results listed in the chart that follows

IgG 153 mg/dL 1-3 years: 507-1,407 mg/dL

IgM576 mg/dL1-3 years: 18-171 mg/dL

IgA11 mg/dL1-3 years: 63-298 mg/dL

IgD 0 mg/dLNewborn to adult: 0-8 mg/dL

IgE1 kIU/L1-3 years: <90 kIU/

2) Why do Bailey's recurring bacterial infections correlate with these laboratory results?

3. What is immunoglobulin isotype switching? How does isotype switching explain the lack ofIgG, IgA, and IgE in Bailey's blood

Answer 1

2) In the above result reduced level of antibodies present in Bailey's blood known as immunodeficient that are more prone to infection, diseases, or allergic reactions than individuals with normal level of antibodies present in their blood and fully developed mmune systems.
Immunoglobulin deficiencies means low level of immunoglobulin (IgG, IgA, IgE) related with an inability to make required antibody. These antibodies are specific immunoglobulin protein that our immune system produced to fight against invading bacteria, fungi,viruses, parasites, or toxins in the body. Every class of antibody binds to their corresponding antigens on the cell surfaces of definite foreign substances, trying to protect the body from illness. When the invading organisms challanged our immune system, different antibodies come into their role to play:

The most abundant class of immunoglobulin is IgG , control towards viruses, bacterial organisms, and toxins. It is present in plasma,some tissue, blood. IgA is activated during early response to bacterial and viral invasion. It is found in saliva, tears, and all other mucus secretions. IgE is present in respiratory secretions and is administered toward parasite invasion also in allergic reactions like atopic dermatitis, hay fever , and allergic asthma.

3) Immunoglobulin isotype switching also known as class switching, or class-switch recombination (CSR), is a process that convert the production of immunoglobulin by  B cell from one type to another, like from the isotype IgM to the isotype IgG. During this process, there is change in constant-region of the heavy chain present in an antibody, and the variable region of the heavy chain remains the same.

In this case IgM concentration is more as compared to IgG, this means that IgM and IgD are the very first antibody that produced while exposure to antigen, and it is producing in adequate amount but what is not happening is that IgM is not converted to IgG i.e. failure of isotype switching occurs. For isotope switching to occur, the activated B cell have to bind the CD40 receptor of T cell and specific cytokines required to be present. The binding of B cell and T cell results in a B cell signal transduction, that switch on isotype switching to generate different antibody isotypes with various functions. If the B cell fails to bind the CD40 receptor or producing cytokines that causes in the loss of propogation of signal transduction and failure of isotype switching, hence producing adequate amount of IgM and IgD but not able to convert in other antibodies that is same happening in the Bailey's blood.