| Abstract: | Previous studies of murine IgM hybridoma protein 18-2-3, derived from an (NZB/NZW)F1 secondary response to fluorescein (FL) presented on T-dependent carrier, demonstrated a high binding affinity for FL (KA = 2.9 X 10(10) M-1) and cryoprecipitation, which could be abrogated upon FL binding. Based on these unusual properties and their possible association with defective immune regulation in lupus-prone mice, further studies were carried out to evaluate the basis of 18-2-3 cryoprecipitation, expression of characteristics related to the 18-2-3 clonotype, and structure/function aspects of additional homogeneous IgM and IgG antibodies of similar origin and specificity. Solubility experiments in which the effect of ionic strength on macroscopic aggregation was measured indicated that 18-2-3 intrinsically possessed both cryoglobulin and euglobulin properties in the absence of auxiliary gamma-globulin components. Rates of hapten fluorescence quenching by 18-2-3 were limited by factors other than diffusion and were dependent on solution temperature and ionic strength. Thirty-seven additional IgM and IgG monoclonal antibodies were shown to possess normal low-temperature solubility and hapten fluorescence-quenching properties, suggesting that 18-2-3 was derived from a relatively rare B cell progenitor. Collective results from FL binding and spectrotype analyses indicated that the majority of proteins were diverse with respect to variable region structure and binding mechanisms but unusually restricted in binding affinities (KA less than 5 X 10(6) M-1). Relative subclass frequencies for 30 monoclonal IgG proteins (IgG1 greater than IgG2b greater than IgG2a greater than IgG3) were consistent with polyclonal IgG subclass expression in normal mice in response to T-dependent immunogen. |
