Apoptosis (Ao), is a process by which cells undergo a form of nonnecrotic cellular suicide. Although for most cells this is a constitutive process, it can be induced in immature and differentiating immune cell populations by stress mediators associated with inflammation. This inducible form of A(o) is referred to as programmed cell death. However, it is not clear whether hematopoietic cell populations such as the thymus and bone marrow are induced to undergo A(o) during polymicrobial sepsis. To assess this, thymocytes, bone marrow cells, or splenocytes (as a source of comparative nonhematopoietic cells) were harvested from C3H/HeN mice at 1, 4, or 24 hours after cecal ligation and puncture (CLP; to induce polymicrobial sepsis) or sham-CLP (Sham). The results showed that mixed bone marrow cells ex vivo, although not to the same extent as thymus, showed a marked increase in the percentage of cells in A(o), increased endonuclease activity, and a significant decrease in cell yield at 24 hours but not at 4 hours after CLP. Similar changes were not evident in splenocytes. Phenotypic, as well as morphologic assessment, indicated that most of the increase in apoptotic cells in the thymus was associated with the immature T cells (CD4+CD8+) and CD8-CD4- cells. In contrast, the increase in bone marrow cell A(o) was associated with only the B220+ cells, with no significant contribution from myeloid cells. Treatment of CLP mice in vivo with either RU-38486 or PEG-(rsTNF- R1)2 was unable to reverse the increased A(o) in the bone marrow of these animals. Taken together, these findings indicate that A(o) as a process induced by polymicrobial sepsis is not limited to the thymus, but can also be detected in the bone marrow. However, unlike thymic A(o), bone marrow is not affected directly/indirectly by glucocorticoids or tumor necrosis factor released during sepsis.
Apoptosis (A O) is a pathological process by which cells undergo a form of inducible nonnecrotic cellular suicide. In vitro studies suggest that changes in the rate of macrophage (Mo) A O may be associated with elevated proinflammatory cytokine secretory capacity, such as interleukin-1 beta (IL-1 beta) (via IL-1 converting enzyme activation). Furthermore, it has been reported that Mo are activated during early (0-4 hours) experimental septic insult to act as sources of proinflammatory cytokines, such as IL-1. However, with the progression of sepsis, these same cells become refractory to further stimulation (appearing dysfunctional). Nonetheless, it remains unknown if this acquired immunosuppression (dysfunction) is associated with an acceleration in macrophage A O. To determine this, male C3H/HeN mice were subjected to sepsis (cecal ligation and puncture, CLP) or sham-CLP and 4 or 24 hours thereafter Mo were isolated from the peritoneum (PMo) and liver (KMo). Macrophage monolayers were lysed either after stimulation with lipopolysaccharide (LPS) (10 microgram/mL, 24 hours) in vitro or immediately (ex vivo) before LPS stimulation and the cytoplasmic cell fraction was retained. The extent of A O was determined using a cell-death enzyme-linked immunosorbent assay, which detects the presence of cytoplasmic oligonucleosomes and changes in the propidium iodide staining intensity. The results indicate that, early after CLP (4 hours) only PMo stimulated with LPS in vitro showed evidence of increasing A O. At 24 hours (late) after the onset of sepsis, the ex vivo extent of A O in PMo was increased but it was decreased in KMo. However, the addition of LPS in vitro results in a marked increase in both septic PMo and KMo A O. This latter result suggests that the inability of Mo to release cytokines in response to stiumulants, such as LPS during late sesis (24 hours), may be because of induciton of accelerated A O in these Mo populations.
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