Tw.~sacmms OF THE ROYAL SOCIETY OF TROPICAL MEDICINE AND HYC~ENE (1991) 85, SUPPLEMENT 1, 17-18

Cytokines in the pathogenesis of bacterial meningitis

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Jussi Mertsola National Public Health Institute, Turku, Finland

Abstract Adjunctive dexamethasone therapy to antibiotic

therapy for bacterial meningitis has been shown in several studies to be beneficial. The roles of inter- leukin 16 and tumour necrosis factor (Y (TNF-or) in bacterial meningitis and in an experimental rabbit model are reviewed; both cytokines play a pivotal role in induction of meningitis. Using dexamethasone with the initial dose of antibiotics caused a decrease in TNF-ar and modulated the in8 ammatory response. Early use of adjunctive dexamethasone is important in therapy of bacterial meningitis.

Despite better antimicrobial agents and advances in medical intensive care technology, the mortality and long-term morbidity rates for children with bacterial meningitis have not significantly changed in the past 20 years. The case-fatality rates for these patients are from 5 to 10% and from 20 to 30% of patients have neurologic sequelae. Hearing loss is the most common neurological complication, occurring in 31% of pa- tients with Streptococcus pneumoniae, 10% in those with Neisseria meningitidis, and 6% in those with Haemophilus injluenzae type b meningitis (COMMIT- TEE ON INFECTIOUS DISEASES, 1990).

Because of these high numbers, other therapeutic approaches that supplement antibiotic treatment have also been evaluated. One of these strategies is steroid therapy. Two studies, done 20 years ago, showed that this type of therapy did not have any significant effect on the nroenosis of meninaitis natients (DE LEMOS & HAGG~RT~, 1969; BELSE? et -al., 1969). Recently, however, 3 prospective, double-blinded, placebo- controlled, randomized studies, done in Dallas, Texas since 1984, have shown positive results, especially by decreasing the incidence of bilateral moderate or greater hearing loss (3% in steroid-treated patients vs 13% in the placebo group) (LEBEL et al., 1988; MCCRACKEN & LEBEL, 1989). In these studies 260 patients were treated with antibiotics plus dexametha- sone 0.6 ma/kg/d for 4 d. or with ulacebo: the dexamethas&eldose used was 3 times higher than that used in an earlier, negative study (BELSEY et al., 1969).

The discovery of the cytokine network has in- creased our understanding of the in&rnrnation pro- cess and has provided a new theoretical basis to explain why this type of therapy could be effective in reducing inflammation and complications in patients with bacterial meningitis. -

At the time of the diagnosis of bacterial meningitis, 95% of patients have detectable interleukin 1-S (IL-1s) concentrations in the cerebrospinal fluid (CSF) (mean 944 pg/ml). Correspondingly, 75% of patients have tumor necrosis factor 01 (TNFo) (mean 787 pg/ml) (MUSTAFA et al., 1989a). From 18 to 30 h later significantly fewer patients who were treated with dexamethasone had raised concentrations of IL-lp, and in those who did the levels were lower

than before treatment; TNFa: concentrations did not differ significantly in the 2 groups. In other studies, done in Dallas, our group was unable to detect TNFa in the CSF of patients with viral or aseptic meningitis, but 89% of these natients had IL-16 (RAWLO et al.. 199Oa). The con&ntrations of IL-16 Were significant~ ly lower than in the bacterial meningitis (mean 48 p ml vs 944 pg/ml). In bacterial meningitis the IL-l $’ concentrations in the CSF at admission were correlated significantly with protein, lactate and TNFor concentrations in the CSF (MUSTAFA et al., 1989a). Patients having more than 500 pg/ml of IL-18 had neuroloeical comnlications sixnificantlv more often. TNFo-concentrations were correlated with CSF protein but not with the rate of neurological complications.

Because TNFar and IL-lJ3 seemed to be of import- ance in these patients, their role in induction of meningitis was further examined using an ex- perimental rabbit model. Anaesthetized rabbits were placed in stereotactic frames and the test materials were directly inoculated into the cisterna magna. Meningitis was induced by H. influenzae type b or its lipo-oligosaccharide (LOS). Purified rabbit TNFar, supplied by Dainippon ‘Pharmaceutical Company (Ianan). was also tested. A cvtolvtic assav with L929 & v&s used for measuremeni of TNFar in CSF samples. Rabbit recombinant IL-lJ3 was obtained from Dr Masaru Yoshinaga (Japan) and IL-lfi concentrations were measured by an enzyme-linked immunosorbent assay.

When H. influenzae type b LOS was injected directly in the cisterna magna of rabbits, only 20 pg were enough to induce meningitis (SYROGIANNO- POULOS et al., 1988). LOS, when injected into the CST;, can induce a release of TNFa: within 45 min, ;vc,; relaches a peak 2 h after the injection (MUSTA-

1989~). Thts response was not dose- dependen; (doses of 2-200 ng) in terms of magnitude or timing. TNFar was not detectable in serum from these animals, suggesting that it was synthesized in the central nervous system. After injection of H. in&enzae type b bacteria, TNFo could not be elicited with the second dose of LOS until 11 h or more after the first LOS inoculation.

Intracisternal injections of TNF~Y induced CSF pleocytos!s m a dose-dependent fashion up to a dose of 10 umts (RAMILO et al., 1990b). In these experi- ments we could also detect IL-lb in the CSF, but only in low concentrations and without consistent peaks. TNFar also increased nrotein and lactate concentra- tions in the CSF. Increased CSF protein is generally considered to reflect increased blood-brain barrier permeability, whereas increased CSF lactate is consi- dered to be a sign of hypoxia in the central nervous system. Anti-TNFar monoclonal antibodies signi- ficantly modulated the inflammatory effects of TNFor.

IL-E3 also induced meningitis in a dose-dewndent fashion up to a dose of ld ng, but IL-lp hid not

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induce TNFa: in these experiments (RAMILO et al., 1990b). Anti-IL-1p antibodies modulated the CSF lactate, protein and white cell increase caused by IL-16. When TNFcw and IL-1S were injected together, they had a synergistic effect corresponding to the effect of H. influenzae tvne b LOS. Antibodies against these 2 cytokmes modaated the infkunmatory effects of LOS but did not have any significant effect on the responses induced bv the other cvtokine.

In conciusion, with this experimental model we have shown that both TNFo and IL-ll3 olav a oivotal role in induction of meningitis. They ha;e ,n&gistic effects and their effects can be modified by their respective antibodies.

We also evaluated, with the same rabbit meningitis model, the effects of the initiation of antibiotic therapy on the inflammation in CSF during bacterial meningitis (MUSTAFA et al., 1989b; MERTSOLA et al., 1989). In these experiments 2x 104-1~ lo5 H. n&en- zue type b organisms were inoculated intracisternally and the rabbits were treated 6 h thereafter with ceftriaxone, ceftriaxone and dexamethasone, or cef- triaxone at 6 h and dexamethasone one hour later. In untreated (control) rabbits the number of bacteria gradually increased during the follow-up period, as did the amount of bacteria-free LOS. which was measured with a chromogenic Limulk assay after filtration of the CSF samples. Ceftriaxone-treated animals had decreased bacterial counts but an exnlo- sive increase in free LOS. A similar increase was found after treatment with chloramphenicol. This release of LOS was associated with a sudden increase of TNFor in the CSF. which did not occur in untreated control rabbits. Antibiotic-treated animals also had an abrupt increase in pleocytosis, and in CSF protein and lactate concentrations. Dexamethasone, given at the same time as the antibiotics, significantly modulated the release of TNFa and the in%rnmatory response, whereas given one hour after the antibiotic it had no effect on the release of TNFar.

Recently, in a prospective study performed in Costa Rica, Dr Carla Odio treated her patients randomly, in a ‘blinded’ fashion, with dexamethasone or placebo 20 min before the first dose of cefotaxime (0~10 et al., 1990). The preliminary results from this study showed significant beneficial effects in steroid-treated patients. There was reduction in lumbar pressure, increase in estimated cerebral perfusion pressure, and decrease in CSF lactate and TNFar concentrations. Patients in the steroid group also had fewer neurolo- gical complications than the control patients.

These results from clinical and experimental stu- dies stress the importance of early treatment with dexamethasone.

In conclusion, it is evident that cytokines have an important role in the pathogenesis of bacterial meningitis. Better understanding of the complex meningeal inflammatory network probably offers several possibilities and strategies for new therapeutic interventions (SAEZ-LLORENS et al., 1990).

Acknowledgement I acknowledge the part played by my colleagues, with

whom I have worked during the last 2 years in Dallas; Dr

George H. McCracken jr, Dr Eric J. Hansen, Dr Octavia Ramilo, Dr Xavier Saez-Llorens, Dr Mahmoud M. Mustafa, Dr Hamid Jafari and Dr Wdham Kennedy.

References Belsey, M. A., Hoffpauir, C. W. & Smith, M. H. (1969).

Dexamethasone in the treatment of acute bacterial meningitis: the effect of the study design in the interpretation of results. Pedianics, 44, 503-513.

Committee of Infectious Diseases (1990). Dexamethasone therapy for bacterial meningitis in infants and children. Pediutrics, 86, 13&133.

De Lemos, R. A. & Haggerty, R. J. (1969). Corticosteroids as an adjunct to treatment in bacterial meningitis: a controlled clinical trial. Pediatrics, 44, 30-34.

Lebel, M. H., Friej, B. J., Syrogiannopoulos, G., Chrane, D. F., Hoyt, M. J., Stewart, S. M., Kennard, B. D., Olsen, K. D. & McCracken, G. H., jr (1988). Dexa- methasone therapy for bacterial meningitis: results of two double-blind, placebo-controlled trials. New Eng- land Journal of Medicine, 319, 964-971.

McCracken, G. H. & Lebel, M. H. (1989). Dexamethasone therapy for bacterial meningitis in infants and children. American Journal of Diseases of Children, 143, 287-289.

Mertsola, J., Ramilo, O., Mustafa, M. M., Saez-Llorens, X., Risser, R. C. & McCracken, G. H., jr (1989). Release of endotoxin after antibiotic treatment of Gram- negative bacterial meningitis. Pediatric Infectious Diseases Joimal, 8, 904-906. -

Mustafa, M. M., Lebel, M.H., Ramilo, O., Olsen, K. D:, Reisch, J. S., Beutler, B. & McCracken, G. H., lr (1989a). Correlation of interleukin-18 and cache&n concentrations in cerebrospinal fluid and outcome from bacterial meningitis. Journal of Pediatrics, 115, 208-213.

Mustafa, M. M., Ramilo, O., Mertsola, J., Risser, R. C., Beutler, B., Hansen, E. J. & McCracken, G. H., jr (1989b). Modulation of infhunmation and cache&n activity in relation to treatment of experimental Haemophilus infbenzae type b meningitis. Journal of Infectious Diseases, 160, 818-825.

Mustafa, M. M., Ramilo, O., Olsen, K. D., Franklin, P. S., Hansen, E. J., Beutler, B. & McCracken, G. H., jr (1989~). Tumor necrosis factor in mediating ex- perimental Huemophilus in@enzue type b meningitis. Journal of Clinical Investigation, 84, 1253-1259.

Odio, C. M., Faingezicht, I., Paris, M., Nassar, F., Saez-Llorens, X., Olsen, K. D. & McCracken, G. H., jr (19%). Double-blinded, randomized, placebo-controlled trial of dexamethasone therapy for bacterial meningitis. Pediatric Research, 27, 178A, abstract 1054.

Ramilo, O., Mustafa, M. M., Porter, J., Saez-Llorens, X., Mertsola, J., Olsen, K. D., Luby, J. P., Beutler, B. & McCracken, G. H., jr (1990a). Detection of interleukin lb but not tumor necrosis factor-o in cerebrospinal fluid of children with aseptic meningitis. Americun Journal of Diseases in Children, 144, 349-352.

Ramilo, O., Saez-Llorens, X., Mertsola, J., Jafari, H., Olsen, K. D., Hansen, E. J., Yoshinaga, M., Ohkawara, S., Nariuchi, H. & McCracken, G. H., jr (1990b). Tumor necrosis factor o/cachectm and interleukin 18 initiate meningeal inflammation. Jouwul of Experimental Medicine, 172, 497-507.

Saez-Llorens, X., Ramilo, O., Mustafa, M. M., Mertsola, J. & McCracken, G. H., jr (1990). The molecular . pathophysiology of bacterial memmgus: current concepts $ft$apeutic imphcauons. 3ournal of Pediatrics, 116,

Syrogiannopoulos, G. A., Hansen, E. J., Erwin, A. L., Munford, R. S., Rutledge, J., Reisch, J. S. & McCrack- en, G. H., jr (1988). Huemophilus influenzae type b lipooligosaccharide induces meningeal inflammation. Journal of Infectious Diseases, 157, 237-244.