Attenuation of the bacterial load in blood by pretreatment with granulocyte-colony-stimulating factor protects rats from fatal outcome and brain damage during Streptococcus pneumoniae meningitis

Abstract

A model of pneumococcal meningitis in young adult rats receiving antibiotics once the infection was established was developed. The intent was to mimic clinical and histopathological features of pneumococcal meningitis in humans. The primary aim of the present study was to evaluate whether medical boosting of the peripheral neutrophil count affected the outcome of the meningitis. The risk of terminal illness over the first 7 days after infection was significantly reduced for rats who had elevated peripheral white blood cell counts after receiving granulocyte-colony-stimulating factor (G-CSF) prior to the infection compared to that for untreated rats (P = 0.039 by the log rank test). The improved outcome was associated with reduced signs of cerebral cortical damage (P = 0.008). Furthermore, the beneficial effects of G-CSF were associated with reduced bacterial loads in the cerebrospinal fluid (median, 1.1 x 10(5) versus 2.9 x 10(5) CFU/ml; P = 0.023) and in blood (median, 2.9 x 10(2) versus 6.3 x 10(2) CFU/ml; P = 0.024), as well as attenuated pleocytosis (median, 800 x 10(6) versus 1,231 x 10(6) cells/liter; P = 0.025), 24 h after the infection. Conversely, initiation of G-CSF therapy 28 h postinfection did not alter the clinical or histological outcome relative to that for non-G-CSF-treated rats. The magnitude of bacteremia and pretreatment with G-CSF were found to be prognostic factors for both outcome and brain damage. In summary, elevated neutrophil levels prior to the development of meningitis result in reduced risks of death and brain damage. This beneficial effect is most likely achieved through improved control of the systemic disease.

FIG. 1.

Quantification of brain damage. (Left) Histological specimens were obtained from the frontal cortex, mid-frontal cortex, and midcortex. (Right) Division of each cerebral hemisphere into five segments for quantification of brain damage. The band of necrosis in the outer cortex layers is indicated by solid arrows.

FIG. 2.

Kaplan-Meier analysis of the G-CSF pretreatment and late-treatment groups compared to the control group (all shown with solid lines). Survival was significantly improved in the G-CSF pretreatment group compared to the control group by the log rank test (P = 0.039). Late G-CSF treatment did not change survival compared to that of the control group. Dashed lines shown for the G-CSF pretreatment group and the control group include both lethal infection and survival with motor sequelae.

FIG. 3.

Comparison between the control group and the G-CSF pretreatment group of WBC counts in cerebrospinal fluid (CSF) and blood. Solid circles, control group; open circles, G-CSF pretreatment group. G-CSF pretreatment increased peripheral-blood WBC counts (P < 0.0001), whereas WBC counts in cerebrospinal fluid were significantly attenuated (P = 0.025) compared to those for the control group.

FIG. 4.

Comparison between the control group and the G-CSF pretreatment group of bacterial concentrations in cerebrospinal fluid (CSF) and blood. Solid circles, control group; open circles, G-CSF pretreatment group. Pretreatment with G-CSF significantly attenuated the bacterial loads in cerebrospinal fluid (P = 0.023) and blood (P = 0.024) compared to those for controls.

FIG. 5.

Brain damage. Brain damage was detected in 20 out of 32 rats in the control group (solid circles) compared to 8 out of 34 in the G-CSF pretreatment group (open circles) and 8 out of 16 in the G-CSF late-treatment group (solid triangles). G-CSF pretreatment significantly reduced brain damage relative to that in the control group (P = 0.008). G-CSF as a late treatment did not reduce brain damage (P = 0.92).

FIG. 6.

Histopathological changes in the cerebral cortices of rats with pneumococcal meningitis. (1) Normal rat brain cortex; (2) prenecrotic lesion with areas of peripheral bleeding; (3 and 4) early necrotic lesions with neuronal loss; (5) necrotic lesion with neutrophil invasion of outer cortex layer; (6) wedge-shaped necrotic lesion; (7) broad band of necrosis; (8) liquefied cortex—total necrosis; (9) vasculitis with halo of edema; (10 and 11) abscess formation; (12) cortical reorganization. Solid arrows, hemorrhages; open arrows, necrotic areas.