Polymorphonuclear leukocyte transit times in bone marrow during streptococcal pneumonia.

The release of polymorphonuclear leukocytes (PMN) from the bone marrow (BM) is a hallmark of acute inflammatory conditions. BM stimulation may increase the toxic potential of these newly released PMN and influence their behavior at inflammatory sites. The present study was designed to measure the transit time of PMN in the mitotic and postmitotic pools of the BM in rabbit using 5'-bromo-2'-deoxyuridine (BrdU). Blood samples were obtained at 2- to 24-h intervals from 24 to 192 h after a single BrdU injection, and BrdU-positive PMN (PMNBrdU) was detected as they appear in the circulating blood, using immunohistochemistry. The intensity of nuclear staining for BrdU was used to define a single generation of PMN and graded as either weakly (G1), moderately (G2), or highly (G3) stained. The mean +/- SE transit time of PMNBrdU through the BM was 95.6 +/- 3.6 h, with 51.1 +/- 5.9 h in the mitotic and 65.4 +/- 5.4 h in the postmitotic pool. Streptococcus pneumoniae instillation in the lung (n = 3) shortened the transit time of PMN through the BM to 54.0 +/- 2.6 h with a shorter time in both the mitotic (36.2 +/- 5.7 h) and the postmitotic pool 34.6 +/- 0.8 h). All these values were shorter than the control values (P < 0.05). We conclude that Streptococcus pneumoniae shortens the transit time of PMN in the mitotic and postmitotic pools in the marrow, which may result in the release of immature PMN with higher levels of lysosomal enzymes into the circulation.