Question

Case study

8-year old girl with recurrent infections caused by Streptococcus pyogenes and Hemophilus influenza was admitted to the hospital following a 5-day sinus infection. Her mother noted that she had developed a productive cough and high fever. Her white blood cell count was 3200/ul (normal count 5000-9000/ul). 25% percent of her white cells were neutrophils (very low), 40% were lymphocytes (normal), and 29% were monocytes (elevated, normal 2 to 8%). A serum test revealed that her IgG level was 35 mg/dl (normal 600-1500 mg/dl), IgA was undetectable (normal 150-225 mg/dl) and her IgM level was 210 mg/dl (normal 75-150 mg/dl). A flow cytometric analysis of her peripheral blood cells revealed that all of her B cells were IgM⁺, IgD⁺.

1. Explain the fact the all patient’s B cells were IgM+, IgD+.

Answer 1

patients with influenza were somewhat more likely to have fever (68% vs 40%), cough (93% vs 80%), and nasal congestion (91% vs 81%) than patients with other infections.In 90% of all patients with probable influenza, lymphopenia and/or monocytosis were present. Relative lymphopenia with or without monocytosis appears to be a laboratory marker for H1N1 virus infection, a finding that could play a major role in early identifying and treating patients with new influenza A. A ratio of lymphocytes to monocytes below 2 is proposed as a screening tool for influenza infection instead of rapid tests.

Immunoglobulin D (IgD) is an antibody isotypethat makes up about 1% of proteins in the plasma membranes of immature B-lymphocytes where it is usually coexpressed with another cell surface antibody called IgM. IgD is also produced in a secreted form that is found in very small amounts in blood serum, representing 0.25% of immunoglobulins in serum.In B cells, IgD's function is to signal the B cells to be activated. By being activated, B cells are ready to take part in the defense of the body in the immune system. During B cell differentiation, IgM is the exclusive isotype expressed by immature B cells. IgD starts to be expressed when the B cell exits the bone marrow to populate peripheral lymphoid tissues. When a B cell reaches its mature state, it co-expresses both IgM and IgD

IgD may have some role in allergic reactions.

Recently, IgD was found to bind to basophilsand mast cells and activate these cells to produce antimicrobial factors to participate in respiratory immune defense in humans.It also stimulates basophils to release B cell homeostatic factors. This is consistent with the reduction in the number of peripheral B cells, reduced serum IgE level and defective primary IgG1 response in IgD knockout mice.

Thus patients B cells were Igm and igd.