Granulocytic stem cell (CFUc) proliferation in experimental group B streptococcal sepsis

Adult rats infected with group B streptococci (GBS) develop neutrophilia and display a marked increase in granulocytic stem cells (CFUc). In contrast, infected neonatal rats develop a profound neutropenia and their CFUc do not increase. In order to better understand this phenomenon, we assessed the CFUc proliferative rate in control and infected adult and neonatal rats using the technique of [3H]-thymidine suicide. Beginning only 3 h after GBS inoculation, adult rats increased CFUc proliferative activity, as illustrated by an increase in thymidine suicide, from 38 +/- 2% cell kill in control animals to 70 +/- 2% when infected (mean + S.E., P less than 0.001). In contrast, the CFUc thymidine suicide rate did not increase in infected neonates. It was noted, however, that the baseline CFUc thymidine suicide rate in uninfected neonatal rats exceeded the rate in uninfected adult rats by 2-3-fold. The CFUc thymidine suicide rate was therefore determined in uninfected premature (74 +/- 1%), newborn (70 +/- 2%), 1-wk-old (70 +/- 1%), 6-wk-old (32 +/- 1%) and 6-month-old (37 +/- 3%) rats. These findings suggest that the proliferative rate of granulocytic stem cells is already maximal or near maximal in noninfected neonatal animals. In contrast to adults, the neonates' granulocyte production from stem cells can not significantly increase, even if bacterial infection is present.