Virus-Specific IgD in Acute Viral Infection of Mice

In phylogenetically diverse species with the help of T lymphocytes or soluble factors, viral infections induce the Ag-specific B lymphocytes to proliferate and terminally differentiate into IgM, IgG, IgA, IgD, or IgE Ab-secreting cells. Based on previous studies searching for IgD, it was inferred that serum IgD in the mouse is nearly undetectable, although in other species, e.g., humans, IgD is a measurable component of serum Ig. More recently, new information has been obtained indicating that IgD is secreted in minute quantities during normal B cell differentiation. We observed that IgD is secreted in significantly increased quantities in mice undergoing an acute infection with lymphocytic choriomeningitis virus or vesicular stomatitis virus compared with uninfected animals. A substantial fraction of the observed IgD was found to be virus specific. Using a solid-phase immunoenzymatic technique, virus-specific IgD Ab-forming cells were detected in the spleen; their numerical increase correlated with the level of secreted antiviral IgD. In addition, immunohistochemical staining revealed IgD⁺ plasma cells that occurred with a similar kinetic profile as the virus-specific IgD Ab-forming cells. These findings provide direct evidence that synthesis of IgD is a physiologic event in the mouse. Its precise function in the immune response to pathogens, however, remains to be determined.