Immunostimulation of C3H/HeJ lymphoid cells by R-chemotype lipopolysaccharide preparations.

Splenocytes from the C3H/HeJ and C57BL/10ScN (nu/nu) inbred mouse strains have been characterized by a genetic defect in their capacity to proliferate in response to purified protein-free LPS preparations. In this manuscript we provide experimental evidence to support the concept that the refractory state of B cells from endotoxin-unresponsive mice to mitogenic stimulation by LPS does not extend to R-chemotype LPS isolated from a variety of rough strains of Salmonella or Escherichia coli. We present several lines of evidence to suggest that the observed mitogenic activity is not the result of contamination of LPS with lipid A-associated proteins. The mitogenic activity of LPS extracted from rough strain mutant bacteria (R-LPS) appears to be dependent upon a structural requirement of the LPS in which the 2-keto-3-deoxyoctulosonate linkage of lipid A with core oligosaccharides is intact. Both alkaline and acid hydrolysis of R-LPS abrogates mitogenic activity in C3H/HeJ splenocytes; only the former is effective in reducing activity of the same LPS preparations in histocompatible normal splenocytes. Finally, we have found that the addition of either polymyxin B or S-chemotype LPS to R-LPS-stimulated C3H/HeJ splenocytes has only minimal effects on the mitogenic activity of the latter. These combined data would indicate that the concept of LPS-unresponsiveness of the C3H/HeJ and C57B1/10ScN inbred mouse strains is not necessarily applicable to all protein-free LPS preparations.