Rabie N. Stephan

Mechanism of immunosuppression following hemorrhage: Defective antigen presentation by macrophages

The mechanism by which simple hemorrhage profoundly impairs the proliferative response of T lymphocytes to mitogen and alloantigen, produces a defect in interleukin-2 generation, and increases the susceptibility to sepsis remains unknown. Since antigen presentation (AP) by the macrophage (M phi) plays a critical role in the antigen-specific activation of T-helper cells and lymphokine production, we investigated whether the function of the M phi as an AP cell is altered following hemorrhage. C3H/HEJ mice were bled to a mean BP of 35 mm Hg, maintained at that level for 1 hr, and then resuscitated. There was no mortality with this model. Control mice were not bled but otherwise treated identically. Immediately after resuscitation the mice were sacrificed and peritoneal M phi (PM phi) as well as splenic adherent cells (SAC) were harvested. AP function was tested by coculturing different numbers of PM phi and SAC with D10.G4.1 cells (2 x 10(4) cells/well) in the presence of conalbumin (300 micrograms/ml). This T-helper cell clone proliferates upon recognition of conalbumin in the context of Iak (a M phi surface membrane glycoprotein), thus directly reflecting M phi AP capability. After 72 hr of incubation, the cultures were pulsed with [3H]thymidine and harvested. D10.G4.1 proliferations induced via AP by PM phi and SAC from hemorrhaged-resuscitated mice were 29 and 24% of control, respectively (P less than 0.05). Thus, we conclude that AP by M phi following hemorrhage is defective despite adequate resuscitation, a mechanism which could explain the state of immunosuppression and enhanced susceptibility to sepsis.

Prostaglandin E2 depresses antigen-presenting cell function of peritoneal macrophages.

Eicosanoids play a prominent role in trauma. Such mediators of inflammation negatively influence cell-mediated immunity (CMI). There is, however, no information available on the effect of eicosanoids on a critical event in CMI, i.e., antigen-presenting (AP) cell function of macrophages (M luminal diameter), a cellular process responsible for the activation of T and B lymphocytes. The aim of this study, therefore, was to examine the effect of prostaglandin E2 (PGE2) and thromboxane B2 (TXB2) on AP cell function of the peritoneal M luminal diameter. To study this, a T-helper-cell clone, D10.G4.1 was employed. This cell clone proliferates in the presence of Iak (Class II glycoprotein, MAC product) bearing M luminal diameter and specific antigen (conalbumin A) thus directly reflecting the AP capability of the M luminal diameter. Peritoneal M luminal diameter were harvested from B10.BR mice (H2k) and their AP was tested in vitro by incubating varying numbers of M luminal diameter with 2 X 10(4) D10.G4.1 cells/well and conalbumin (400 micrograms/ml) in the presence and absence of different concentrations of PGE2 or TXB2. Cultures were incubated for 72 hr, pulsed with [3H]-thymidine, and harvested. At concentrations of 10, 30, and 100 nM of PGE2, D10.G4.1 proliferations were 38, 35, and 20% of control, respectively (P less than 0.05 compared to control). TXB2 added at the above-mentioned concentrations did not suppress the proliferative response of D10. Thus, PGE2 but not TXB2 has a potent immunosuppressive effect on AP of peritoneal M luminal diameter.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular dysfunction in sepsis

Abstract Sepsis produces a characteristic hypermetabolic and hyperdynamic circulatory state. If this response is not reversed, multiple organ failure follows with a high mortality rate. The cellular dysfunction that results in overt organ failure is not clear. Changes in oxygen delivery and consumption in septic patients have raised questions concerning the adequacy of cellular energy stores to maintain cellular function and integrity. Animal septic models have, however, allowed direct determinations of adenosine triphosphate (ATP) and mitochondrial function and correlation with other measurements of cell function. In fact, studies indicate that cellular energy stores and mitochondrial function are well-maintained at a time when cellular abnormality can be demonstrated. In early sepsis, is, 10 hours following cecal ligation and puncture, abnormalities in cell membrane function and membrane potential are present, while ATP levels are maintained. In addition, although there is an absolute increase in the rate of gluconeogenesis, the response to substrate and hormonal stimulation in isolated perfused liver from rats in early sepsis is altered. In late sepsis, is, 16 hours after cecal ligation and puncture, ATP levels decrease and lactate increases. These findings are consistent with tissue hypoxia resulting from hypoperfusion in late sepsis. Thus, it appears that cellular functions are adversely affected in early sepsis, suggesting that the persistence of deleterious effects of sepsis, if not reversed, may lead to organ failure. Certainly, when hypoperfusion occurs in this setting, cellular energy stores appear to decrease, increasing the risk of organ failure and death.

Post-OKT3 induction therapy CD complex response predicts renal allograft rejection

CD complex response to cessation of induction with OKT3 may be predictive of rejection. Twenty-seven patients receiving renal allografts and OKT3 induction immunosuppression were retrospectively analyzed for CD complex repopulation and allograft rejection. Flow cytometric monitoring was utilized in all patients. Responder status groups were identified based on CD complex repopulation, with fast responders demonstrating CD complex repopulation above the determined cohort mean. Slow responders had repopulation below this mean. Students t test yielded P<0.01 (CD2), P<0.02 (CD3), and P<0.01 (CD8). Nonresponder patients were identified with repopulation below the mean, but flat compared with depletion. All nine fast responders lost their graft or were treated for rejection. No slow responder experienced graft loss or rejection episodes. One nonresponder was treated for rejection. CD complex activity following OKT3 cessation correlates with future rejection. Identification of responder status provides insight into propensity to reject, allowing individual tailoring of immunosuppression to patient response.