The C3H/HeJ mouse strain, previously shown to be a nonresponder to bacterial lipopolysaccharide (LPS)-induced mitogenesis in vitro, was demonstrated by the present studies to be competent to respond mitogenically to LPS, but only to LPS preparations obtained by selected extraction methods. These preparations appear to be confined to LPS isolated by mild extraction techniques, such as TCA or butanol. In contrast, those obtained by techniques utilizing phenol were only weakly stimulatory or completely nonstimulatory for spleen cells from the C3H/HeJ. All LPS preparations tested, on the other hand, were highly stimulatory for cells from another mouse strain, namely the C3H/St. The critical importance of the method of extraction of LPS on its mitogenic activity for C3H/HeJ cells was stressed by experiments in which LPS was prepared from Escherichia coli K235 using either of two procedures. In these experiments, phenol-extracted LPS, although mitogenic in the C3H/St, was completely nonstimulatory in the C3H/HeJ; whereas, butanol-extracted LPS was highly stimulatory in both strains of mice. This striking difference was attributed to a destructive effect of phenol on LPS, as demonstrated by the fact that treatment of butanol LPS with phenol resulted in a total loss of its mitogenic activity in the C3H/HeJ, but in only a partial loss in the C3H/St. In general, the mitogenic response observed with selected LPS preparations in the C3H/HeJ was quantitatively lower and more transient than that seen with the C3H/St, although qualitatively these responses appeared to be similar. This was evidenced by the observation that in both mouse strains LPS was a specific mitogen for B cells, a property which was also attributed in both strains to the same distinct structural region of the LPS molecule, that is lipid A. A preparation of LPS that failed to stimulate B cells from the C3H/HeJ nonetheless had the capacity to block activation of these B cells by a stimulatory preparation of LPS. These results strongly suggest that mitogenic stimulation of B cells by LPS is a function of the structural integrity of both the LPS molecule and putative B-cell receptors for LPS.

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