Risk factors associated with nausea and vomiting in children with cancer receiving chemotherapy.

INTRODUCTION: Despite treatment with antiemetic medications, nausea remains uncontrolled for many children receiving chemotherapy. One reason is that risk factors for nausea in children remain poorly explored. The purpose of this study was to identify risk factors for chemotherapy-induced nausea (CIN) in children. METHODS: Prospective, observational study including 101 children (median age 6.4 years, range 0.8-17.9) with cancer receiving moderately or highly emetogenic chemotherapy. Primary endpoints were complete control of acute and delayed CIN, defined as no nausea in the acute phase 0-24 h after chemotherapy and in the delayed phase starting after the acute phase and ending 5 days later. Multivariable analyses included age, sex, cancer type, susceptibility to motion sickness, chemotherapy duration, numbers of antiemetics, co-administration with opioids or tricyclic antidepressants, and previously uncontrolled nausea or vomiting. RESULTS: Acute CIN was associated with susceptibility to motion sickness (odds ratio [OR] 5.73, 95% confidence interval [CI] 1.36-33.7) and older age (OR 4.19, 95% CI 1.30-14.7), comparing age group 8-18 years with 0-3 years. Delayed CIN was associated with uncontrolled acute nausea or vomiting (OR 10.3, 95% CI 2.65-50.9), highly emetogenic chemotherapy (OR 8.26, 95% CI 1.17-76.8), and having a hematologic cancer type (OR 7.81, 95% CI 1.05-79.2). CONCLUSIONS: Susceptibility to motion sickness and age can influence the risk of acute CIN. More research is needed on how best to integrate risk information in preventive antiemetic strategies. Sufficient acute nausea and vomiting control are crucial to prevent delayed CIN.

TCERG1L allelic variation is associated with cisplatin-induced hearing loss in childhood cancer, a PanCareLIFE study.

In children with cancer, the heterogeneity in ototoxicity occurrence after similar treatment suggests a role for genetic susceptibility. Using a genome-wide association study (GWAS) approach, we identified a genetic variant in TCERG1L (rs893507) to be associated with hearing loss in 390 non-cranial irradiated, cisplatin-treated children with cancer. These results were replicated in two independent, similarly treated cohorts (n = 192 and 188, respectively) (combined cohort: P = 5.3 × 10-10, OR 3.11, 95% CI 2.2-4.5). Modulating TCERG1L expression in cultured human cells revealed significantly altered cellular responses to cisplatin-induced cytokine secretion and toxicity. These results contribute to insights into the genetic and pathophysiological basis of cisplatin-induced ototoxicity.

Cryopreservation of ovarian tissue for fertility preservation in a large cohort of young girls: focus on pubertal development.

STUDY QUESTION: Is there an association between the need for medical puberty induction and the diagnosis or treatment received in girls who have undergone cryopreservation of ovarian tissue for fertility preservation? SUMMARY ANSWER: There was a clear association between the intensity of treatment received and requirement for medical puberty induction but no association with the diagnosis. WHAT IS KNOWN ALREADY: Although it cannot be predicted which girls will become infertile or develop premature ovarian insufficiency (POI) following intensive chemotherapy or irradiation, patients who are at high risk of POI should be offered ovarian tissue cryopreservation (OTC). This includes girls who are planned to receive either high doses of alkylating agents, conditioning regimen before stem cell transplantation (SCT), total body irradiation (TBI) or high radiation doses to the craniospinal, abdominal or pelvic area. STUDY DESIGN, SIZE, DURATION: This is a retrospective cohort study. In total, 176 Danish girls under 18 years of age have had OTC performed over a period of 15 years. An overview of the girls' diagnoses and mean age at OTC as well as the number of deceased is presented. Of the 176 girls, 38 had died and 46 girls were still younger than 12 years so their pubertal development cannot be evaluated yet. For the 60 girls who had OTC performed after 12 years of age, the incidence of POI was evaluated and in the group of 32 girls who were younger than 12 years at OTC, the association between the diagnosis and received treatment and the requirement for medical puberty induction was examined. PARTICIPANTS/MATERIALS, SETTING, METHODS: The need for medical puberty induction was assessed in 32 girls who were prepubertal at the time of OTC. MAIN RESULTS AND THE ROLE OF CHANCE: Indications for OTC were allogeneic SCT for leukaemia, myelodysplastic syndrome or benign haematological disorders, autologous SCT for lymphoma or sarcoma, and irradiation to the pelvis or to the spinal axis. The mean age at OTC of the 176 girls were 11.3 years. The two most prevalent diagnoses of the 176 girls were malignant tumours and malignant haematological diseases. Among the 32 prepubertal girls, 12 received high dose chemotherapy and either TBI prior to SCT or irradiation to the pelvis, abdomen or the spinal axis, 13 received high dose alkylating agents but no irradiation prior to SCT, six received alkylating agents as part of conventional chemotherapy and one patient had a genetic metabolic disorder and did not receive gonadotoxic treatment. Among these 32 girls, 23 did not undergo puberty spontaneously and thus received medical puberty induction. Among the nine girls, who went through spontaneous puberty, four had received high dose alkylating agents and five had received conventional chemotherapy. LIMITATIONS REASONS FOR CAUTION: All information was retrieved retrospectively from patient records, and thus some information was not available. WIDER IMPLICATIONS OF THE FINDINGS: OTC should be recommended to all young girls, who present a high risk of developing ovarian insufficiency and/or infertility following high dose chemotherapy and/or irradiation. STUDY FUNDING/COMPETING INTERESTS: The Childhood Cancer Foundation (2012-2016) and the EU interregional project ReproHigh are thanked for having funded this study. They had no role in the study design, collection and analysis of the data or writing of the report. The authors have no conflict of interest to disclose.

Increased risk of antidepressant use in childhood cancer survivors: a Danish population-based cohort study.

AIM: Childhood cancer survivors are at risk of both somatic and mental late effects, but large population-based studies of depression are lacking. METHODS: Risk of antidepressant use was evaluated in a population-based cohort of 5452 Danish children treated for cancer in 1975-2009 by linkage to the National Prescription Drug Database, which worldwide is the oldest nationwide registry of prescription medication. Hazard ratios (HRs) for antidepressant use were estimated in a Cox proportional hazards model stratified on sex, with population comparisons as referents. RESULTS: Overall, childhood cancer survivors were at increased risk of having antidepressants prescribed (HR, 1.4; 95% confidence interval (CI), 1.3-1.5). The excess absolute risk of antidepressant use was 2.5 per 1000 person-years (95% CI, 1.7-3.3), equivalent to an excess of 2.5 survivors for every 100 survivors followed for 10years. Increased HRs of 30-50% were seen for survivors of cancers of all main groups (haematological malignancies, central nervous system (CNS) and solid tumors); the highest risk was among children treated with haematopoietic stem cell transplantation (HR, 1.9; 95% CI, 1.2-3.1). Our data suggested that the risk was most pronounced for children treated in the most recent calendar periods (test for interaction between cancer and calendar periods: P<0.001), especially for survivors of haematological cancers (P=0.007). Interaction analysis of the effect of parental socioeconomic position and psychiatric disease on the association between childhood cancer and antidepressant use indicated no modifying effect. CONCLUSION: Childhood cancer survivors should be followed-up for depression. Our results indicate an increasing need for follow-up especially in survivors treated by more recent, intensive anticancer treatment.

A 10-year follow up of reproductive function in women treated for childhood cancer.

Previously, this study group found that female childhood cancer survivors could be at risk of early cessation of fertility. The aim of the present study was to evaluate reproductive function in the same group of survivors 10 years after the initial study. Of the original cohort of 100, 71 were re-examined. Thirty-six survivors reported regular menstrual cycles. When they were compared with 210 controls, they differed significantly in antral follicle count (AFC) (median 15 versus 18, P=0.047) but not in anti-Müllerian hormone (AMH) (median 13.0 versus 17.8 pmol/l). Survivors cured with minimal gonadotoxic treatment had significantly higher AMH and AFC compared with survivors cured with either potentially gonadotoxic treatment or treatment including alkylating chemotherapy and ovarian irradiation (20.0, 5.8 and <3 pmol/l, P<0.001; and 15, 9 and 2, P=0.03, respectively). Thirty-eight survivors had achieved at least one live birth. Complicated second-trimester abortions (n=4) were observed primarily in survivors cured with radiotherapy affecting pelvic organs. In conclusion, childhood cancer survivors have signs of diminished ovarian reserve. However, if the ovarian function is preserved in the early to mid-twenties, it is likely to persist until the mid-thirties, giving a good chance of childbearing.

Unchanged incidence and increased survival in children with neuroblastoma in Denmark 1981-2000: a population-based study.

Treatment results for neuroblastoma in Denmark have been poorer than in other Nordic countries, so we investigated whether a change in incidence, stage distribution and survival had occurred between 1981 and 2000. Clinical data were retrieved from the medical charts of 160 children <15 years of age with extra-cranial neuroblastoma (n=139) or ganglioneuroblastoma (n=21) diagnosed in Denmark between 1981 and 2000. The minimal follow-up time was 52 months. Statistical analyses were performed in STATA. The incidence was 8.55 per million children below 15 years of age (world standard 9.6) and 42.6 per million children below 12 months of age, and it has remained unchanged since 1970. The median age at diagnosis was 27 months. In all, 32% of the children were aged below 12 months at diagnosis, 53% had metastatic disease and in 12% the diagnosis was made incidentally. Prognostic factors such as age, stage and site of primary tumour were the same as in other studies and did not change. During the study period, the mortality rate decreased steadily, and the 5-year survival rate increased from 38% in 1981-1985 to 59% in 1996-2000, corresponding to the level found in other Western countries. Increased survival was also seen in children with metastatic disease. Participation in international studies, better supportive care and possibly postoperative autologous stem cell transplantation may have contributed to the increased survival.

G(2) chromosomal radiosensitivity in Danish survivors of childhood and adolescent cancer and their offspring.

In order to investigate the relationship between chromosomal radiosensitivity and early-onset cancer, the G(2) chromosomal radiosensitivity assay was undertaken on a group of 23 Danish survivors of childhood and adolescent cancer, a control group comprising their partners and a group of 38 of their offspring. In addition, the previously reported in-house control group from Westlakes Research Institute (WRI) was extended to 27 individuals. When using the 90th percentile cutoff for the WRI control group, the proportion of individuals with elevated radiosensitivity was 11, 35, 52 and 53% for the WRI control, partner control, cancer survivor and the offspring groups, respectively, with significant differences between the WRI control group and the cancer survivor group (P=0.002) and the offspring group (P<0.001). However, while the comparisons with the WRI control group support an association of chromosomal radiosensitivity with cancer predisposition, when the partner control group was used to define the radiosensitivity cutoff point, no significant differences in radiosensitivity profiles were found between the partner control group and either the cancer survivor group or the offspring group. The failure to distinguish between the G(2) aberration profiles of the apparently normal group of partners and the cancer survivor group suggests that any association with cancer should be viewed with caution, but also raises questions as to the suitability of the partners of cancer survivors to act as an appropriate control group. Heritability of the radiosensitive phenotype was examined by segregation analysis of the Danish families and suggested that 67.3% of the phenotypic variance of G(2) chromosomal radiosensitivity is attributable to a putative major gene locus with dominant effect.

Glucagon-like peptide-2 (GLP-2) response to enteral intake in children during anti-cancer treatment.

BACKGROUND: Intestinal dysfunction is frequent in cancer and during anti-cancer treatment. Glucagon-like peptide-2 (GLP-2) is secreted in a nutrition-dependent manner from the intestinal enteroendocrine L-cells. It accelerates crypt cell proliferation and nutrient absorption, inhibits enterocyte apoptosis and decreases mucosal permeability. Lack of GLP-2 may increase the risk of malabsorption and intestinal bacterial translocation. The aim of this study is to evaluate meal stimulated secretion of GLP-2 in children with cancer undergoing anti-cancer treatment. METHODS: Plasma-GLP-2 analysis after an overnight fast and 1 hour after intake of a mixed test meal. Data on gastrointestinal toxicity, blood neutrophile counts and food records were included in the analysis. RESULTS: Forty-four meal stimulation tests were performed in 25 children (median age, 6.0 years; range, 2.5-19) during anti-cancer treatment. Median GI toxicity score was 5 (range, 0-15), and mean energy intake was 62.4% of recommended values. P-GLP-2 values increased from mean (SD) 38 (18) to 63 (51) pmol/l (P < 0.0001). Twelve of the meal stimulation tests (28%) resulted in a p-GLP-2 increase >2 fold, which is assumed to be the lower limit of normal values. The increase was strongly dependent on the energy intake (r = 0.62, P < 0.0001), while toxicity score and neutrophile count had no significant influence (multiple regression). CONCLUSION: In children treated with anti-cancer therapy, GLP-2 secretion seems to be normal if the enteral energy intake is sufficient. Insufficient GLP-2 secretion could influence the gastrointestinal problems seen in the children with a low enteral energy intake.

Diminished ovarian reserve in female childhood cancer survivors with regular menstrual cycles and basal FSH <10 IU/l.

BACKGROUND: Approximately 70% of children treated for cancer are cured, however the treatment often impairs reproductive function. The aim of the present study was to assess ovarian reserve in women with an apparently normal ovarian function, who were cured of cancer in childhood. METHODS: Twenty-one female survivors with regular menstrual cycles and basal FSH <10 IU/l were included. The control group included 21 healthy age-matched regularly cycling women. On cycle day 2-5, ovarian volume and number of small antral follicles (2-5 mm) were evaluated with transvaginal ultrasonography. Repeated sonography, urinary LH testing, and endocrine assessments were performed during the actual cycle. Cycle length was calculated. RESULTS: The female survivors had significantly smaller volume per ovary (4.9 versus 6.8 cm(3); P < 0.01), a lower number of small antral follicles per ovary (4.5 versus 8.0; P < 0.01), and lower total number of follicles per ovary (8 versus 11, P < 0.01). Hormonal profiles were similar, but the mean cycle length of the female survivors was significantly shorter than in the control group (28.3 versus 31.0 days; P < 0.05). CONCLUSIONS: Childhood cancer survivors with regular menstrual cycles and basal FSH <10 IU/l seem to have a diminished ovarian reserve. Consequently, they may have a shortened reproductive span and an early menopause.

Primitive neuroectodermal tumor of the orbit in a 5-year-old girl with microphthalmia.

PURPOSE: To report an orbital, intraconal, primitive neuroectodermal tumor (PNET) in a 5-year-old child with microphthalmia since birth. METHODS: Orbitotomy was performed and a large, polycystic, retroscleral, intraconal tumor was removed and subsequent histological, immunohistochemical and electron-microscopic analyses of the excised mass were performed. RESULTS: The tumor showed characteristic features of peripheral primitive neuroectodermal tumor including pseudorosettes, positive immunohistochemical reactions for the MIC2 gene and synaptophysin and ultrastructural finding of neurosecretory granules. CONCLUSION: This case is the first reported intraconal PNET of the orbit, and the first orbital case that expresses the MIC2 gene. In spite of the aggressive malignant features of peripheral PNET, the orbital variety seems to be the least aggressive since most of the reported patients are still alive.

Monoclonal antibodies with neuroblastoma specificity: a flow cytometric analysis of cross-reactivity with CD34+ hematopoietic stem cells.

The aim of this study was to evaluate the specificity of a number of monoclonal antibodies (MAbs) used for immunological in vitro purging of stem cell grafts from neuroblastoma patients. The extent of cross-reactivity of 10 neuroblastoma-specific MAbs (NB-MAb) with CD34+ stem cells from 14 leukapheresis products was analyzed. The level of cross-reactivity was analyzed on a Coulter (Fullerton, CA) flow cytometer using biotinylated NB-MAbs. There was a marked difference in the reactivity of the ten NB-MAbs with CD34+ stem cells. The antibodies could be divided into three groups with increasing levels of cross reactivity. Four antibodies (126-4, 5.1 H11, UJ127.11, and 14.G2a) all reacted with median levels of less than 2% (range 0.0 to 5.4) of CD34+ stem cells (median of 14 patients). Another three antibodies reacted with a median of 3.1-4.1% of the stem cells (UJ13A, Ab390, and Ab459) but with a wide range (0.2 to 25.6). Finally, M340, HSAN 1.2, and antiThy-1 reacted with a median of 9-16% of the stem cells (range 0.6 to 51.5). We conclude that there is a significant variation in the proportion of CD34+ stem cells reacting with each of the ten neuroblastoma antibodies investigated in this study. Therefore, to avoid a significant loss of CD34+ cells from the stem cell product, we find it important to carefully consider which antibodies to use for immunomagnetic purging.

Feasibility of neonatal screening for toxoplasma infection in the absence of prenatal treatment. Danish Congenital Toxoplasmosis Study Group .

BACKGROUND: The best method for prevention and control of congenital toxoplasma infection is uncertain. Prenatal screening is done in Austria and France, but the effect of treatment during pregnancy is not well documented. The aim of our study was to find out the maternofetal transmission rate and outcome in infants born to mothers who were not treated during pregnancy. METHODS: We analysed 89873 eluates from phenylketonuria (PKU) cards from neonates and paired first-trimester serum samples from the mothers for specific IgG antibodies to Toxoplasma gondii. Children born to mothers who seroconverted during pregnancy were followed-up clinically and serologically to 12 months of age. In addition, 21144 PKU cards were analysed for toxoplasma-specific IgM antibodies during the last 12 months of the study. FINDINGS: In 24989 (27.8%) cases both the PKU eluate and the first-trimester samples were IgG positive, which indicates previous maternal infection. 139 of the 64884 seronegative women acquired toxoplasma infection during pregnancy and gave birth to 141 infants (two sets of twins). 27 of these children were diagnosed with congenital toxoplasma infection. The transmission rate was 19.4% (95% CI 13.2-27.0). Clinical signs and symptoms were found in four (15%) of the 27 children. The additional analysis for toxoplasma-specific IgM antibodies from the PKU card identified seven of nine children with congenital toxoplasma infection. The false-positive rate for the IgM test was 0.19 per 1000, and no false-negatives were found. INTERPRETATION: The risks of transmission of infection and of disease in the infant are low in an area with a low risk of toxoplasma infection. A neonatal screening programme based on detection of toxoplasma-specific IgM antibodies alone will identify between 70% and 80% of cases of congenital toxoplasmosis.

[Malignant solid tumors in children]. / Maligne solide tumorer hos børn.

The outcome of malignant solid tumours in children has clearly improved during the last 20 years, as a result of more precise diagnosis and assessment of tumour spread, more intensive combination treatment including pre- and postoperative chemotherapy as well as improved surgical and anesthesia techniques, radiotherapy and supportive care. This review describes newer diagnosis and treatment methods for the different types of solid tumours in children. Lastly, the actual strategies for further improvement, with focus on late effects of therapy, are presented.

An increased loading dose of ondansetron: a north european, double-blind randomised study in children, comparing 5 mg/m2 with 10 mg/m2.

A North European, randomised, double-blind study, comparing a loading-dose of ondansetron of 5 mg/m2 with 10 mg/m2, administered intravenously before highly emetogenic chemotherapy, was carried out in 187 chemotherapy-naïve children. In the first 24 h, both groups received further ondansetron intravenously at a dose of 5 mg/m2 8-hourly. Thereafter, ondansetron was given at an oral dose of 4 or 8 mg depending on the surface area of the child, three times a day and continued for at least 3 days after the last day of chemotherapy. There was no difference in the control of emesis between the two groups. Ondansetron provided good control of emesis and nausea on day 1 with 71-72% of patients experiencing two or fewer emetic episodes (complete or major responders) and 90-86% of patients reporting nausea as none or mild. There was also no difference in the efficacy of the treatment arms in the control of emesis and nausea on subsequent days of the study period. Both anti-emetic regimens were well-tolerated.

Effect of Legionella pneumophila sonicate on killing of Listeria monocytogenes by human polymorphonuclear neutrophils and monocytes.

Legionella pneumophila shares with other intracellular pathogens the ability to resist intracellular killing within phagocytes. An increasing number of cellular components of L. pneumophila are proposed as pathogenic factors of the organism. At the site of infection, the phagocytic cells will be exposed to bacterial components, either expressed on the surface of the organisms or released in the environment upon cell lysis. In this study, we have investigated the effect of water-soluble bacterial components present in L. pneumophila sonicate on the phagocytosis and bactericidal activity of human polymorphonuclear neutrophils and monocytes. Preincubation of neutrophils with L. pneumophila sonicate did not affect phagocytosis of L. monocytogenes, whereas Listeria killing was significantly inhibited at sonicate concentrations of 1 and 2 mg/ml. The phenol phase of a phenol-water extraction, containing most of the lipopolysaccharide (LPS), had no inhibitory effect on the listericidal activity of neutrophils. Killing of Listeria by monocytes was inhibited in a similar manner. The inhibitory activity was mainly recovered in the sonicate fraction above 100 kDa, suggesting that components organized in larger molecular complexes are most likely to represent the inhibitory factors. The inhibitory activity of L. pneumophila sonic extract appears to be related to inhibition of killing mechanisms since uptake of Listeria was not affected by the sonicate. Our observations indicate that as Legionella infection progresses, bacterial components liberated by cell lysis could exert a detrimental effect on the antimicrobial function of phagocytes, stressing the importance of early treatment of Legionnaires' disease to reduce bacterial numbers in the infected tissues.

Demonstration of the intracellular production of tissue-destructive protease by Legionella pneumophila multiplying within guinea-pig and human alveolar macrophages.

The major extracellular enzyme of Legionella pneumophila, a metalloprotease, has been proposed as a pathogenic factor in Legionnaires' disease due to its cytotoxic, tissue-destructive, and phagocyte-inhibitory properties. The relevance of these activities depends on the production of the protease during infection, i.e. by L. pneumophila multiplying intracellularly. In this study, L. pneumophila was demonstrated to produce protease in guinea-pig and human alveolar macrophages infected in vitro. After 24 h infection, approximately 0.1 to 0.2 micrograms of protease per 10(6) bacteria was measured by ELISA in culture supernatants and lysates of the infected cells, whereas no protease could be detected immediately after infection. Immunogold labelling using anti-protease antibody showed the enzyme to be located within phagosomes and distributed throughout the macrophages. Recent observations have shown that this protease could modify host defence mechanisms through inhibition of bacterial killing by neutrophils and monocytes. The intracellular production of the enzyme in infected macrophages demonstrated here further supports a role for the protease in the pathogenesis of Legionnaires' disease.

Effect of Legionella pneumophila cytotoxic protease on human neutrophil and monocyte function.

The extracellular metalloprotease of Legionella pneumophila, also called tissue-destructive protease or major secretory protein, has been proposed as one of the virulence factors of this organism. Considering the decisive role played by the phagocytic cells in host defense against Legionella infection, we investigated the effect of this protease on the function of human neutrophils and monocytes. L. pneumophila protease inhibited the chemotactic response of neutrophils to F-Met-Leu-Phe and zymosan-activated serum in a concentration-dependent and heat-labile manner. A direct effect of the protease on the chemotactic activity of neutrophils was demonstrated by the continued inhibition of neutrophil chemotaxis when the protease was removed following pre-incubation of the cells. In contrast, the enzyme had no effect on monocyte chemotaxis. The protease inhibited, also in a concentration-dependent and heat-labile manner, the binding of F-Met-Leu-Phe to both cell types. Neutrophil and monocyte oxidative burst response, as measured by superoxide release and chemiluminescence response, was not significantly affected by the enzyme. A slight enhancement of PMA-stimulated superoxide release was induced by the protease in both cell types. Lastly, the protease inhibited the killing of Listeria monocytogenes by neutrophils or monocytes. Inhibition of Listeria killing was concentration-dependent, heat-labile, and did not require the presence of the enzyme in the bactericidal assay. The inhibitory activity of L. pneumophila protease on neutrophil chemotaxis and on the listericidal activity of human neutrophils and monocytes demonstrated in this study provides evidence for a role of this enzyme in the pathogenesis of Legionnaires' disease.

Prevalence of IgM antibodies to nine Legionella species in Icelandic children.

In order to evaluate the prevalence of antibodies to Legionella species among children in Iceland, a prospective study was conducted in 424 children aged 1 month to 12 years, 28 of whom had an acute respiratory tract infection. Antibody titers to L. pneumophila serogroup 1-6, L. bozemanii, L. dumoffii, and L. micdadei were measured by microagglutination technique. Seroreactivity to Legionella spp. was found in 30% of the children greater than 3 years of age and in 22% of all children. The majority of the children with legionella antibodies had no history of previous or present respiratory tract infection. The children with previous pneumonia or bronchial asthma did not show a higher seroreactivity to legionella than children without such a history. Our observations suggests that Icelandic children are frequently exposed to Legionella species or closely related bacteria.

Inhibition of human natural killer cell activity by Legionella pneumophila protease.

The present study was undertaken to define the effect of Legionella pneumophila protease on natural killer (NK) cell function in vitro. Lysis of target cells by human NK cells was determined using a 51Cr-release assay. The protease inhibited the NK cell cytolytic activity in a concentration- and time-dependent manner. The inhibitory effect of the protease was not affected by alpha interferon or interleukin 2. Legionella pneumophila protease partly inhibited the binding of effector cells to target cells as studied in a single cell agarose assay of monocyte-depleted cell populations. This effect of the protease on the binding of NK cells to target cells could interfere with the previously described enhanced NK cell activity induced by Legionella pneumophila. We could demonstrate in vitro inhibition of NK cell activity by Legionella pneumophila protease at very low concentrations, suggesting a possible relevance of this mechanism in the pathogenesis of Legionnaires' disease.