Hemopoietic effects in mice of a lipid A-associated protein.

The effects of the bacterial cell-wall components (BCWC) lipid A and lipid A-associated protein (LAP) on humoral and cellular hemopoietic parameters were investigated in mice. Both lipid A and LAP increased serum levels of granulocyte-macrophage colony-stimulating factors (CSF) in C57BL/6 mice. In C3H/HeJ mice the CSF responses to lipid A and LAP were 7 and 3 fold less than the corresponding CSF responses found in C3H/GSF mice. Both BCWC increased the numbers of splenic multipotential hemopoietic stem cells (CFUS) as well as colony-forming cells (CFC) for neutrophilic granulocytes, macrophages, eosinophils and megakaryocytes. Lipid A but not LAP caused a marked decrease in the femoral numbers of B lymphocyte colony-forming cells (BL-CFC). The Bl-CFC incidence in the spleen or in the mesenteric lymph node changed little if at all after injection of either of the two BCWC. Morphological analysis of marrow cells showed an increase in the proportion of myeloid cells and a concomitant decrease in the proportion of erythroid precursor cells after injection of both BCWC. In the spleen, lipid A but not LAP caused an increase in the proportion of myeloid cells, erythroid precursor cells and plasma cells. In all experiments where both BCWC showed activity, lipid A was more potent than LAP on a weight basis.