CD200R1 promotes interleukin-17 production by group 3 innate lymphoid cells by enhancing signal transducer and activator of transcription 3 activation

Psoriasis is a common chronic inflammatory skin disease with no cure. It is driven by the interleukin (IL)-23/IL-17A axis and type 17 T helper cells; however, recently, group 3 innate lymphoid cells (ILC3s) have also been implicated. Despite being the focus of much research, factors regulating the activity of ILC3s remain incompletely understood. Immune regulatory pathways are particularly important at barrier sites, such as the skin, gut, and lungs, which are exposed to environmental substances and microbes. CD200R1 is an immune regulatory cell surface receptor that inhibits proinflammatory cytokine production in myeloid cells. CD200R1 is also highly expressed on ILCs, where its function remains largely unexplored. We previously observed reduced CD200R1 signaling in psoriasis-affected skin, suggesting that dysregulation may promote disease. Here, we show that contrary to this, psoriasis models are less severe in CD200R1-deficient mice due to reduced IL-17 production. Here, we uncover a key cell-intrinsic role for CD200R1 in promoting IL-23-driven IL-17A production by ILC3s by promoting signal transducer and activator of transcription 3 activation. Therefore, contrary to its inhibitory role in myeloid cells, CD200R1 is required on ILC3 to promote IL-23-stimulated signal transducer and activator of transcription 3 activation, triggering optimal IL-17 production.

Phenotypically distinct anti-insulin B cells repopulate pancreatic islets after anti-CD20 treatment in NOD mice

AIMS/HYPOTHESIS

Autoreactive B cells escape immune tolerance and contribute to the pathogenesis of type 1 diabetes. While global B cell depletion is a successful therapy for autoimmune disease, the fate of autoreactive cells during this treatment in autoimmune diabetes is unknown. We aimed to identify and track anti-insulin B cells in pancreatic islets and understand their repopulation after anti-CD20 treatment.

METHODS

We generated a double transgenic system, the VH125.hCD20/NOD mouse. The VH125 transgenic mouse, expressing an increased frequency of anti-insulin B cells, was crossed with a human CD20 (hCD20) transgenic mouse, to facilitate B cell depletion using anti-CD20. B cells were analysed using multiparameter and ImageStream flow cytometry.

RESULTS

We demonstrated that anti-insulin B cells were recruited to the pancreas during disease progression in VH125.hCD20/NOD mice. We identified two distinct populations of anti-insulin B cells in pancreatic islets, based on CD19 expression, with both populations enriched in the CD138^int fraction. Anti-insulin B cells were not identified in the plasma-cell CD138^hi fraction, which also expressed the transcription factor Blimp-1. After anti-CD20 treatment, anti-insulin B cells repopulated the pancreatic islets earlier than non-specific B cells. Importantly, we observed that a CD138^intinsulin⁺CD19^- population was particularly enriched after B cell depletion, possibly contributing to the persistence of disease still observed in some mice after anti-CD20 treatment.

CONCLUSIONS/INTERPRETATION

Our observations may indicate why the loss of C-peptide is only temporarily delayed following anti-CD20 treatment in human type 1 diabetes.

PTEN and PIK3CA gene copy numbers and poor outcomes in non-small cell lung cancer patients with gefitinib therapy

METHODS

Fluorescent in situ hybridisation analyses of PTEN, PIK3CA, EGFR and CEN7 were performed on tumour specimens from patients treated on the expanded access gefitinib trial. Progression-free survival (PFS) and overall survival (OS) were correlated with outcomes in all patients and EGFR wild-type patients.

RESULTS

Progression-free survival (hazard ratio=2.54, P<0.001) and OS (hazard ratio=4.04, P<0.001) were significantly shorter in patients whose tumours had all of the following molecular patterns: CEN7 <4 copies per cell, PTEN loss (<2 copies in at least 20% of cells), and PIK3CA gain (>2 copies in at least 40% of cells) both in all and EGFR wild-type only patients.

CONCLUSION

The combination of low CEN7 copy number, PTEN loss, and PI3KCA gain may be useful for identifying NSCLC patients unlikely to benefit from treatment with EGFR (TKIs), specifically in wild-type EGFR cases.

Clinical and molecular characteristics of advanced non-small cell lung cancer (NSCLC) patients (pts) with rapid progressive disease (RPD) on gefitinib therapy (G)

7592

Background: Prognostic factors associated with better outcomes (EGFR mutations (mut), high EGFR gene copy number, never smoking) can be used to select pts for EGFR tyrosine kinase inhibitor (TKI) combination trials, but would exclude the majority of NSCLC pts. Excluding pts with the worst likely outcomes is another strategy that may result in more pts who could benefit from the combination of a TKI with other agents. Our objective was to identify clinical and molecular characteristics associated with RPD (=70 days) and shorter progression-free survival (PFS) in previously treated NSCLC pts receiving G. Methods: Consecutive Expanded Access Trial pts with >1 week G were included for analysis. Tissue from 87 pts was evaluated for EGFR, pAKT and PTEN protein expression by immunohistochemistry; 58 tumors were analyzed for mut and sum of CA dinucliotide repeats (ΣCA rpts) by SSCP, PCR and sequencing. Results: There were 150 pts; 77 female, median (md) age 67. Md follow-up was 5.8 months (mo). Objective response was 8% (2CR, 10PR, 56 SD, 82 RPD). Md Kaplan-Meier PFS and survival were 2.0 and 5.8 mo, respectively. See table for univariate results. Smoking, Mut-PTEN-, EGFR-PTEN- and EGFR-pAKT- tumors were associated with shorter PFS. Separate clinical and molecular multivariate models were developed. In logistic regressions, non-adenocarcinoma histology (N- A), p=0.004, =12 mo from diagnosis to G (dx-G =12 mo), p=0.0009, lack of mut (p=0.0298) and ΣCA rpts <34 (p=0.0622) were associated with RPD. In Cox regressions, N-A (p=0.0256), dx-G =12 mo (p=0.0166) and lack of mut (p=0.0298) were associated with shorter PFS. Conclusions: N-A, dx-G =12 mo and lack of mut were associated with RPD and shorter PFS in univariate and multivariate analyses. ΣCA rpts <34 and double-negative molecular combinations were also related to worse outcome. These clinical and molecular characteristics may warrant further study as exclusion criteria for TKI combination clinical trials.

[Table: see text] [Table: see text]

EGFR mutations (muts), IHC and FISH status, and chromosome 7 gene copy number combined with pAkt expression as potential predictors of survival in non-small cell lung cancer (NSCLC) patients (pts) treated with gefitinib (GEF)

7182

Background: EGFR and pAkt expression by immunohistochemistry (IHC), muts, and FISH status have been identified as possible molecular predictors for GEF efficacy in NSCLC (Cappuzzo, et. al, JNCI, 2005). The goal of this study was to independently evaluate these findings regarding survival (surv), and to assess the predictive value of mean chromosome 7 copy number/cell (C7). Methods: 150 consecutive Expanded Access Trial pts with >1 week GEF therapy were included for analysis. IHC (present vs not detected) was performed for 87 pts, and 58 pts were analyzed for muts by SSCP, mut-specific PCR, and sequencing. Tissue from 81 pts was evaluated for EGFR and C7 gene copy numbers by fluorescence in situ hybridization (FISH). Results: 150 pts (77 female, 73 male; median (md) age 67; 85 adenocarcinoma) received GEF; md follow-up was 5.8 months (mo). Overall response was 8% (2 CR, 10 PR); 56 pts had stable disease. Md Kaplan-Meier surv was 5.9 mo. IHC revealed that 47/87 pts (54%) had EGFR+, and 36/75 pts (48%) had pAkt + tumors. pAkt+ pts had significantly (sig) longer surv than pAkt− pts (11.4 vs 5.8 mo, p < .05). High polysomy was seen in 36/81 pts (44%) who were designated FISH+; 45 pts were FISH−. EGFR IHC and FISH positivity were not sig associated with surv. C7 was defined as low (<3.6, 63 pts) or high (≥3.6, 18 pts); md surv was 6.6 and 17.1 mo, respectively, p < .01. Muts were found in 17/58 tumors (29%). Md surv for pts with and without muts was 23.8 and 7.9 mo, respectively, p < .07. EGFR IHC− pAkt− pts (18 pts) had sig shorter surv than 57 pts with any pos value (4.7 vs 8.8 mo, p < .02). Double-positive pts had sig longer surv than pts with any neg value. Conclusions: These findings resemble but do not duplicate those reported by Cappuzzo, et al. Additionally, high C7, alone or combined with pAKT, may be an important predictor for GEF efficacy in NSCLC. Further studies of C7, a technically simple and reproducible FISH assay, are warranted.

[Table: see text]

[Table: see text]

Gastrointestinal hemorrhage in advanced non-small cell lung cancer (NSCLC) patients treated with erlotinib and celecoxib

7172

Background: Erlotinib (E) was associated with superior survival in a phase III trial of previously treated advanced NSCLC patients (pts). Celecoxib (C) has been shown to potentiate the apoptotic and growth inhibitory effects of E in pre-clinical models. Methods: This was a phase II trial of E plus C in advanced NSCLC pts that failed one prior chemotherapy regimen. Primary endpoint: efficacy; secondary endpoint: toxicity. Pts received C (400mg b.i.d.) and E (150mg daily) until disease progression. Planned accrual: 40 pts. Results: 26 pts with stage IIIB/IV NSCLC were enrolled. Patient (pt) characteristics: male 65%; median age 66; ECOG performance status 0/1- 96%. Eighteen pts had tissue available for FISH and EGFR mutation analysis: 50% had chromosome 7 polysomy (> 4 copies per cell); none had EGFR gains (>2 EGFR/chromosome 7). Two pts had an EGFR gene mutation (1 exon 19, 1 exon 21). Response results: partial response- 2 pts (1 with exon 19 mutation), stable disease- 8 pts, and progressive disease- 16 pts (1 with exon 21 mutation). Median progression free survival (PFS) and overall survival (OS): 1.9 and 10.2 months, respectively. Grade 3/4 upper gastrointestinal bleeding (GIB) occurred in 4 pts prompting study closure. One pt was on therapeutic dalteparin and two pts receiving warfarin developed marked INR prolongation (INR >10). The fourth pt had a history of peptic ulcer disease. Platelet counts at time of GIB: 142 - 559. Three pts had endoscopy and gastric or duodenal ulcers were found in all three cases. No pts were taking anti-acid medication at the time of GIB. No other pts were on therapeutic anticoagulation. Three pts without upper GIB were taking low-dose aspirin. Other toxicities: 85% grade 1/2 rash; 65% grade 1/2 diarrhea, 30% grade 1/2 nausea, 30% grade 1/2 fatigue (one grade 3 fatigue); one grade 3 pneumonitis, one grade 3 esophageal stricture. Conclusions: These observations suggest that C plus E may be associated with increased incidence of gastrointestinal ulceration and GIB and that the regimen should not be given to pts with a previous history of peptic ulcer disease or to pts requiring therapeutic anticoagulation. Based on response rate, PFS, and OS in this group of pts, it appears that results with E and C are similar to those reported for E alone.

[Table: see text]

Gene expression in chronic lymphocytic leukemia B cells and changes during induction of apoptosis

Our studies in chronic lymphocytic leukemia (CLL) are directed at understanding which signals maintain viability in vivo and become lost upon removal of leukemic cells from the body, such that they immediately begin to undergo apoptosis ex vivo. In this report, we examine changes in gene expression observed between freshly isolated CLL B cells and after maintenance in vitro with and without Fludara. We compare these effects with an Epstein-Barr virus (EBV)-transformed cell line treated similarly. Kinetic effects of drug treatment on apoptosis and cell division were examined with DNA laddering, radioisotopic labeling, and flow cytometry using the fluorescent dye carboxyfluorescein diacetate succinimidyl ester. Reverse transcriptase polymerase chain reaction and hybridization blots of microarray cDNA analyses were performed to examine gene expression. We demonstrate that many genes, especially cyclin D1, were downregulated after culture of CLL cells. Anti-apoptotic genes BAG-1 and Akt2 were upregulated. The greatest positive effect with Fludara was the upregulation of JNK1. The EBV-transformed cell line was resistant to classic DNA laddering induced with Fludara. Although DNA synthesis was blocked, the EBV-transformed cell line had some ability to recover from treatment following drug washout. CLL cells express cell cycle regulatory genes that are specific for activated cells in the G(1)-S phase of the cell cycle. Growth regulatory signals are lost when the leukemic cells are isolated from the body. Fludara enhances kinetics of apoptosis and induces expression of a gene responsive to stress that regulates expression of a kinase involved in initiation of the apoptotic pathway.

Activation of the LRP (lung resistance-related protein) gene by short-term exposure of human leukemia cells to phorbol ester and cytarabine

Treatment-induced secondary drug resistance of tumor cells is a major cause of relapsed disease and therapeutic failure in cancer patients. It has been shown that the expression of the multidrug resistance MDR1/P-glycoprotein gene could be induced by short-term in vitro exposure of cells to protein kinase C (PKC) agonists or different chemotherapeutic drugs. We studied whether other genes involved in drug resistance are regulated by similar signaling pathways. Transient (up to 24 h) treatment of HL-60 or K562 leukemia cells with phorbol 12-myristate 13-acetate (TPA) resulted in increased steady-state level of LRP (lung resistance-related protein) mRNA and protein. Among conventional chemotherapeutic drugs tested, only cytarabine (Ara C) induced the LRP mRNA expression though no increase in LRP protein was detected. LRP gene activation was not detectable in either H9 T-cell leukemia or in solid carcinoma cell lines (BT-20, ZR-75-1, and SW 1573). None of the agents influenced the levels of MRP (multidrug resistance-associated protein) mRNA in any cell line tested. In HL-60 cells, the LRP activation by TPA or Ara C was sustained for at least 23 days after withdrawal of inducing agents. bis-Indolylmaleimide I, a potent PKC inhibitor, attenuated TPA-induced LRP activation. In contrast, the inhibitor had no effect on the LRP induction by Ara C. These data indicate that the LRP gene can be activated by different mechanisms, some of which involve PKC.

Stress ulcer prophylaxis in critically ill patients. Resolving discordant meta-analyses

PURPOSE

To resolve discrepancies in previous systematic overviews and provide estimates of the effect of stress ulcer prophylaxis on gastrointestinal bleeding, pneumonia, and mortality in critically ill patients.

DATA IDENTIFICATION

Computerized search of published and unpublished research, bibliographies, pharmaceutical and personal files, and conference abstract reports.

STUDY SELECTION

Independent review of 269 articles identified 63 relevant randomized trials for inclusion.

DATA ABSTRACTION

We made independent, duplicate assessment of the methodologic quality, population, intervention, and outcomes of each trial.

RESULTS

The source of discrepancies between prior meta-analyses included incomplete identification of relevant studies, differential inclusion of non-English language and nonrandomized trials, different definitions of bleeding, provision of additional information through direct correspondence with authors, and different statistical methods. The current overview demonstrates that prophylaxis with histamine2-receptor antagonists decreases the incidence of overt gastrointestinal bleeding (odds ratio [OR], 0.58; 95% confidence interval [CI], 0.42 to 0.79) and clinically important bleeding (OR, 0.44; 95% CI, 0.22 to 0.88). There is a trend toward decreased overt bleeding when antacids are compared with no therapy (OR, 0.66; 95% CI, 0.37 to 1.17). Histamine2-receptor antagonists and antacids are associated with a trend toward lower clinically important bleeding rates than sucralfate is. There is a trend toward an increased risk of pneumonia associated with histamine2-receptor antagonists as compared with no prophylaxis (OR, 1.25; 95% CI, 0.78 to 2.00). Sucralfate is associated with a lower incidence of nosocomial pneumonia when compared with antacids (OR, 0.80; 95% CI, 0.56 to 1.15) and histamine2-receptor antagonists (OR, 0.77; 95% CI, 0.60 to 1.01). Sucralfate is also associated with a reduced mortality rate (OR, 0.73; 95% CI, 0.54 to 0.97) relative to antacids and to histamine2-receptor antagonists (OR, 0.83; 95% CI, 0.63 to 1.09).

CONCLUSIONS

Our results emphasize the need for registries to include all randomized trials and demonstrate the importance of explicit methodology for systematic reviews. There is strong evidence of reduced clinically important gastrointestinal bleeding with histamine2-receptor antagonists. Sucralfate may be as effective in reducing bleeding as gastric pH-altering drugs and is associated with lower rates of pneumonia and mortality. However, the data are insufficient to determine the net effect of sucralfate compared with no prophylaxis.

Stress ulcer prophylaxis in critically ill patients. Resolving discordant meta-analyses

PURPOSE

To resolve discrepancies in previous systematic overviews and provide estimates of the effect of stress ulcer prophylaxis on gastrointestinal bleeding, pneumonia, and mortality in critically ill patients.

DATA IDENTIFICATION

Computerized search of published and unpublished research, bibliographies, pharmaceutical and personal files, and conference abstract reports.

STUDY SELECTION

Independent review of 269 articles identified 63 relevant randomized trials for inclusion.

DATA ABSTRACTION

We made independent, duplicate assessment of the methodologic quality, population, intervention, and outcomes of each trial.

RESULTS

The source of discrepancies between prior meta-analyses included incomplete identification of relevant studies, differential inclusion of non-English language and nonrandomized trials, different definitions of bleeding, provision of additional information through direct correspondence with authors, and different statistical methods. The current overview demonstrates that prophylaxis with histamine2-receptor antagonists decreases the incidence of overt gastrointestinal bleeding (odds ratio [OR], 0.58; 95% confidence interval [CI], 0.42 to 0.79) and clinically important bleeding (OR, 0.44; 95% CI, 0.22 to 0.88). There is a trend toward decreased overt bleeding when antacids are compared with no therapy (OR, 0.66; 95% CI, 0.37 to 1.17). Histamine2-receptor antagonists and antacids are associated with a trend toward lower clinically important bleeding rates than sucralfate is. There is a trend toward an increased risk of pneumonia associated with histamine2-receptor antagonists as compared with no prophylaxis (OR, 1.25; 95% CI, 0.78 to 2.00). Sucralfate is associated with a lower incidence of nosocomial pneumonia when compared with antacids (OR, 0.80; 95% CI, 0.56 to 1.15) and histamine2-receptor antagonists (OR, 0.77; 95% CI, 0.60 to 1.01). Sucralfate is also associated with a reduced mortality rate (OR, 0.73; 95% CI, 0.54 to 0.97) relative to antacids and to histamine2-receptor antagonists (OR, 0.83; 95% CI, 0.63 to 1.09).

CONCLUSIONS

Our results emphasize the need for registries to include all randomized trials and demonstrate the importance of explicit methodology for systematic reviews. There is strong evidence of reduced clinically important gastrointestinal bleeding with histamine2-receptor antagonists. Sucralfate may be as effective in reducing bleeding as gastric pH-altering drugs and is associated with lower rates of pneumonia and mortality. However, the data are insufficient to determine the net effect of sucralfate compared with no prophylaxis.

Reversal of multidrug resistance phenotype by surfactants: relationship to membrane lipid fluidity

Previous studies have suggested that multidrug resistance (MDR) reversal by polyoxyethylene surfactants involves alterations in plasma membrane lipid physical state of resistant cells as one of the possible mechanism(s). To date, however, a detailed and critical examination of the relationship between membrane lipid fluidity and MDR reversal by these surfactants has not been performed. In the present studies, therefore, a series of experiments were conducted to critically examine the role of membrane lipid physical state in MDR reversal by employing a unique class of clinically important nontoxic lipophilic surfactants and the KB-8-5-11 drug-resistant cell line. MDR reversal was assessed by rhodamine-123 uptake. The effect of surfactants on plasma membrane lipid fluidity of these cells was assessed utilizing a fluorescence polarization technique with fluorophores DPH, TMA. DPH, 2-AS, and 12-AS. Our studies demonstrated that: (i) in vitro addition of active MDR-reversing surfactants (Solutol HS-15, Tween 40, and Cremophor EL, 10 micrograms/ml each) decreased lipid fluidity of isolated crude plasma membranes of resistant cells; (ii) the inactive surfactants (octylglucoside, hecameg) failed to influence membrane lipid fluidity; (iii) cells grown in the presence of active surfactants also exhibited a decreased plasma membrane lipid fluidity as measured with intact cells utilizing the probe TMA.DPH; and (iv) active surfactants did not influence lifetimes of the excited state of the fluorophores. These findings demonstrate that decrease of the plasma membrane lipid fluidity of KB 8-5-11 resistant cells may be one of the important mechanism(s) of MDR reversal by polyoxyethylene surfactants.

Approximate dimensions of membrane lesions produced by streptolysin S and streptolysin O

Membrane lesions produced by the streptococcal membranolysins streptolysin S and streptolysin O were investigated. Escape of labeled marker molecules of various sizes from resealed sheep erythrocyte ghosts treated with the toxins for 30 min allowed estimation of the sizes of the primary channels formed. Streptolysin S formed lesions ranging in size up to 45 A in diameter, and even high toxin concentrations did not result in larger channels. The lesions produced by streptolysin O exceeded 128 A in diameter. Kinetics experiments demonstrated that the primary streptolysin O lesions were formed rapidly (1-2 min), but release of marker molecules from streptolysin S-treated vesicles began only after a 5-15-min lag period. Label release from large unilamellar liposomes treated with streptolysin S suggested that membrane fluidity does not affect the size of the streptolysin S lesions.

Effect of streptolysin S on liposomes. Influence of membrane lipid composition on toxin action

The effect of the bacterial cytolytic toxin, streptolysin S, on liposomes composed of various phospholipids was investigated. Large unilamellar vesicles containing [14C]sucrose were prepared by reverse-phase evaporation, and membrane damage produced by the toxin was measured by following the release of labeled marker. The net charge of the liposomes had little or no effect on their susceptibility to steptolysin S and the toxin was about equally effective on liposomes composed of phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and phosphatidylglycerol. Experiments with liposomes composed of synthetic phospholipids showed that the ability of the toxin to produce membrane damage depended on the degree of unsaturation of the fatty acyl chains. The order of sensitivity was C18 : 2 phosphatidylcholine greater than C18: I phosphatidylcholine greater than C18 : 0 phosphatidylcholine = C16 : 0 phosphatidylcholine. Liposomes containing the latter two phospholipids were virtually unaffected by streptolysin S, and experiments with C18 : 0 phosphatidylcholine suggested that toxin activity does not bind to liposomes composed of phospholipids with saturated fatty acyl chains. The inclusion of 40 mol% cholesterol in C16 : 0 phosphatidylcholine and C18 : 0 phosphatidylcholine liposomes made these vesicles sensitive to streptolysin S. Egg phosphatidylcholine liposomes, which were unaffected at 0 degrees C and 4 degrees C became susceptible to the toxin at these temperatures when cholesterol was included. Liposomes composed of C14 : 0 phosphatidylcholine were unaffected by streptolysin S at temperatures below the chain-melting transition temperature (23 degrees C) of this phospholipid, but became increasingly susceptible above this temperature. The results suggest that the fluidity of the phospholipid hydrocarbon chains in the membrane is important in streptolysin S action.

Resistance to streptolysin O in mammalian cells treated with oxygenated derivatives of cholesterol. Cholesterol content of resistant cells and recovery of streptolysin O sensitivity

Cultures of L cells and HeLa cells were made resistant to the cytolytic toxin, streptolysin O, by incubating them in the presence of 20 alpha-hydroxycholesterol or 25-hydroxycholesterol. Such cells were also found to be more resistant to the cytotoxic effects of saponin and digitonin, agents known to interact with membrane cholesterol. Sterol synthesis in L cells that had been treated with either of the oxygenated derivatives of cholesterol was reduced by almost 90%, and the free cholesterol content of streptolysin O-resistant HeLa and L cells fell to approx. 50% of control cell levels. Significant recovery of sensitivity to streptolysin O occurred in about 6 h when refractory L cells were incubated in serum or cholesterol. Partial recovery was observed when the cultures were incubated for 24 h in mevalonate or lipid-depleted serum. The results provide further support for the role of membrane cholesterol in the cytotoxic action of streptolysin O on mammalian cells.

Increased resistance to streptolysin O in mammalian cells treated with oxygenated derivatives of cholesterol

L-cell fibroblast cultures were treated with certain oxygenated derivatives of cholesterol which are known to inhibit cholesterol biosynthesis in mammalian cells. After incubation in the presence of 20-alpha-hydroxycholesterol or 25-hydroxycholesterol for 18 h, the cells became increasingly resistant to streptolysin O. Maximum resistance to toxin was obtained by incubation for 48 h in 0.5 microgram of 20-alpha-hydroxycholesterol or 0.25 microgram of 25-hydroxycholesterol per ml; under these conditions, the cells were 10 to 50 times more resistant than were untreated controls. The ability of the hydroxycholesterol compounds to render the cells resistant was related to the age of the cultures. Maximum protection was found when more sparsely populated cultures were treated with 25-hydroxycholesterol. Older, heavily populated cultures could not be protected even with the high concentrations of 25-hydroxycholesterol. In contrast to control cultures, most of the toxin activity remained in the medium after being incubated with hydroxycholesterol-treated cultures. The results indicate that less toxin binds to the resistant cells and suggest that a reduction in membrane cholesterol content may account for resistance to streptolysin O.

Effects of streptolysin O on transport of amino acids, nucleosides, and glucose analogs in mammalian cells

The transport of several amino acids, nucleosides, and glucose analogs was studies in HeLa cells treated with sublethal concentrations of streptolysin O. A differential effect of toxin on the various solutes tested was observed. The uptake of the neutral amino acids alanine, alpha-aminoisobutyric acid, leucine, and phenylalanine was reduced by 60 about to 70%. Less inhibition of transport was observed with acidic and basic amino acids, and the uptake of nucleosides and glucose analogs was reduced by 20% or less. The decreased uptake of alpha-aminoisobutyric acid could be explained by the inability of toxin-treated cells to retain this amino acid. The altered transport of phenylalanine and lysine, however, appeared to be due to decreased initial rates of uptake rather than to the loss of these amino acids from intracellular pools in toxin-treated cells. After treatment with sublethal concentrations of streptolysin O, the cells recovered their ability to transport and accumulate alpha-aminoisobutyric acid in about 4 h. The data suggest that the alterations in membrane transport observed in toxin-treated cells are due to an effect of streptolysin O on specific transport systems, rather than to the production of holes or pores in the membrane.