Dysregulation of immune response following neurosurgical operations

Epigenetic landscapes suggest that genetic risk for intracranial aneurysm operates on the endothelium

BACKGROUND

Genetics play an important role in intracranial aneurysm (IA) pathophysiology. Genome-wide association studies have identified several single nucleotide polymorphisms (SNPs) that are linked to IA but how they affect disease pathobiology remains poorly understood. We used Encyclopedia of DNA Elements (ENCODE) data to investigate the epigenetic landscapes surrounding genetic risk loci to determine if IA-associated SNPs affect functional elements that regulate gene expression and if those SNPs are most likely to impact a specific type of cells.

METHODS

We mapped 16 highly significant IA-associated SNPs to linkage disequilibrium (LD) blocks within the human genome. Within these regions, we examined the presence of H3K4me1 and H3K27ac histone marks and CCCTC-binding factor (CTCF) and transcription-factor binding sites using chromatin immunoprecipitation-sequencing (ChIP-Seq) data. This analysis was conducted in several cell types relevant to endothelial (human umbilical vein endothelial cells [HUVECs]) and inflammatory (monocytes, neutrophils, and peripheral blood mononuclear cells [PBMCs]) biology. Gene ontology analysis was performed on genes within extended IA-risk regions to understand which biological processes could be affected by IA-risk SNPs. We also evaluated recently published data that showed differential methylation and differential ribonucleic acid (RNA) expression in IA to investigate the correlation between differentially regulated elements and the IA-risk LD blocks.

RESULTS

The IA-associated LD blocks were statistically significantly enriched for H3K4me1 and/or H3K27ac marks (markers of enhancer function) in endothelial cells but not in immune cells. The IA-associated LD blocks also contained more binding sites for CTCF in endothelial cells than monocytes, although not statistically significant. Differentially methylated regions of DNA identified in IA tissue were also present in several IA-risk LD blocks, suggesting SNPs could affect this epigenetic machinery. Gene ontology analysis supports that genes affected by IA-risk SNPs are associated with extracellular matrix reorganization and endopeptidase activity.

CONCLUSION

These findings suggest that known genetic alterations linked to IA risk act on endothelial cell function. These alterations do not correlate with IA-associated gene expression signatures of circulating blood cells, which suggests that such signatures are a secondary response reflecting the presence of IA rather than indicating risk for IA.

The Quantitative and Functional Changes of Postoperative Peripheral Blood Immune Cell Subsets Relate to Prognosis of Patients with Subarachnoid Hemorrhage: A Preliminary Study

OBJECTIVE

It has been suggested that the preoperative (PRE) and postoperative (POST) immune system alteration triggered by aneurysmal subarachnoid hemorrhage (SAH) and surgical treatment itself may affect patients' prognosis and contribute to POST complications. The mechanisms may be attributed to immune suppression-triggered infection or immune overreaction-triggered aseptic inflammation. In this study, we investigated the dynamic changes in peripheral immune cell subsets as well as the alterations of inflammatory cytokines in patients with aneurysmal SAH who received craniotomy and clipping surgery. In addition, we studied the association of those changes with POST complications and clinical prognosis.

METHODS

We investigated 27 patients who received craniotomy and clipping surgery for aneurysmal SAH. The operations were all performed within 24 hours after the occurrence of aneurysm rupture. Detailed immune monitoring (peripheral blood leukocytes and lymphocyte subsets and inflammatory cytokines) was performed on PRE (on admission), day 1, day 3, and day 6 after operation.

RESULTS

Our data showed that the percentage of CD3+, CD8+, natural killer T (NKT), CD4+, and regulatory T (Treg) cells significantly decreased and the level of interleukin 4 (IL-4), interferon γ, and IL-2 significantly increased 1 day after surgery compared with the data in PRE. On the contrary, natural killer (NK), NK group 2 (NKG2D), and B cells increased and the level of IL-10 in plasma decreased. In study of the relationship between POST fever and the change in immune cell subgroups, the fever group had a lower percentage of CD3+, CD4+, NKT, Tregs, and B cells on day 1, day 3, and day 6 after surgery compared with the patients who did not have fever, whereas the CD8+, NK, and NKG2D subsets showed the opposite trend. Furthermore, we analyzed the association between immune profile changes and the prognosis of those patients. The patients were divided into those with an unfavorable prognosis (n = 6) and those with a favorable prognosis (n = 21) according to Glasgow Outcome Scale score and postoperation (POST) coma. Our results showed that except for B cells, patients with a favorable prognosis had a relatively higher percentage of CD3+, CD4+, CD8+, NK, NKT, NKG2D, and Treg cells compared with the unfavorable prognosis group from PRE to day 6 POST.

CONCLUSIONS

Our results indicated that patients with aneurysmal SAH undergoing craniotomy and clipping surgery had a profound transient deterioration in immune function. In addition, the changes in immune cell subgroups had a strong association with POST fever. The changes in immune cell subgroups were also directly associated with clinical prognosis of the patients. These association findings might be attributable to a better biomarker to predict patient diagnosis.

Nosocomial bloodstream infections in neurosurgery: a 10-year analysis in a center with high antimicrobial drug-resistance prevalence

BACKGROUND

Data on nosocomial bloodstream infections (NBSI) in neurosurgery is limited. This study aimed to analyze the epidemiology, microbiology, outcome, and risk factors for death in neurosurgical patients with NBSI in a multidrug resistant setting.

METHODS

Neurosurgical patients with a confirmed NBSI within the period 2003-2012 were retrospectively analyzed. NBSI was diagnosed when a pathogen was isolated from a blood sample obtained after the first 48 h of hospitalization. Patients' demographic, clinical, and microbiological data were recorded and analyzed using univariate and multivariate analysis.

RESULTS

A total of 236 patients with NBSI were identified and 378 isolates were recovered from blood cultures. Incidence of NBSI was 4.3 infections/1000 bed-days. Gram-negative bacteria slightly predominated (54.5 %). The commonest bacteria were coagulase-negative staphylococci (CoNS, 26 %), Klebsiella pneumoniae (15.3 %), Pseudomonas aeruginosa (14.8 %), and Acinetobacter baumannii (13.2 %). Carbapenem resistance was found in 90 % of A. baumannii, in 66 % of P. aeruginosa, and in 22 % (2003-2007) to 77 % (2008-2012) of K. pneumoniae isolates (p < 0.05). Most CoNS and Staphylococcus aureus isolates (94 and 80 %, respectively) were methicillin-resistant. All Gram-negative isolates were sensitive to colistin and all Gram-positive isolates were sensitive to vancomycin and linezolid. Antimicrobial consumption decreased after 2007 (p < 0.05). Overall mortality was 50.4 %. In multivariate analysis, advanced age and stay in an Intermediate Care Unit (IMCU) were independent risk factors for in-hospital mortality (p < 0.05).

CONCLUSIONS

Overall, high incidence of NBSI and considerable resistance of Gram-positive and particularly Gram-negative bacteria were noted in neurosurgical patients. Mortality was high with advanced age and stay in IMCU being the most important death-related factors.

Hydrogel-coated ventricular catheters for high-risk patients receiving ventricular peritoneum shunt

Shunt infection is a morbid complication of cerebrospinal fluid (CSF) shunting. The catheters with a hydrophilic surface may impede bacterial adherence and thereby reduce catheter-related CSF infection.A retrospective study compared the occurrence of CSF infection related to use of either standard silastic catheters or hydrogel-coated ventricular catheters (Bioglide, Medtronic). The enrolment was available to neurosurgery patients undergoing shunt surgery from October 2012 to 2015 in two centers. The follow-up period was more than months.A total of 78 patients were included in the study. In 33 patients 35-cm hydrogel-coated ventricular peritoneum shunts (VPS) were used, and in remaining 45 patients 35-cm standard silastic VPS catheters were used. Infection occurred in 14 (17.9%) patients, including definite VPS-related CSF infection in 6 patients (7.7%) and probable infection in remaining 8 patients (10.3%). There was a significant difference found in patients with total infection between the two groups [RR (95% CI); 0.200 (0.050-0.803), P = 0.014]. Analysis of Kaplan-Meier curve estimates indicated significant statistical difference between the two catheter types in duration (log rank = 4.204, P < 0.05). Significant statistical differences were also found in the subgroups including previous CSF infection within 1 month (log rank = 4.391, P = 0.04), conversion of external ventricular drains to shunt (Log Rank = 4.520, P = 0.03), and hospital stay >1 month (log rank = 5.252, P = 0.02). There was no difference found between the two groups of the patients with other infections within 1 month. The follow-up period was of 36 months.The hydrogel-coated catheter is a safe and related to lower infection rates for high-risk patients who underwent shunt surgery.

Intracranial malignant lesions correlate with the requirement for a long treatment course in postoperative central nervous system infection

AIM

Our aim was to study the clinical features of postoperative meningitis after neurosurgery and identify the factors affecting the duration of treatment.

METHODS

This retrospective study assessed 283 patients with postoperative bacterial meningitis in the Neurosurgery Department of Beijing Tiantan Hospital, Beijing, People's Republic of China, between January and December 2012. Patients' clinical data were reviewed, and multivariate logistic regression analysis was used to identify the factors associated with a prolonged treatment course.

RESULTS

The mortality rate was 0.4% in these patients, of whom 12.4% were found with pathogens in the cerebrospinal fluid. Among the three most common pathogens detected were methicillin-resistant Staphylococcus aureus, Acinetobacter baumannii, and Pseudomonas aeruginosa. The mean treatment course was 13.5±2.1 days. Interestingly, the treatment duration for postoperative meningitis was significantly longer in patients with intracranial malignant tumors than in those with benign lesions. Single-factor analysis showed that male sex (P=0.042) and malignant (rather than benign) lesions (P<0.001) were significantly associated with prolonged treatment duration. Multivariate analysis further confirmed that malignant intracranial lesions represented an independent risk factor for prolonged treatment duration (odds ratio: 2.5962; 95% confidence interval: 1.1092-6.6134).

CONCLUSION

The nature of the intracranial lesion is an independent risk factor for the duration of treatment in postoperative meningitis after neurosurgery.

Epidemiology and genetics of intracranial aneurysms

Intracranial aneurysms are acquired lesions (5-10% of the population), a fraction of which rupture leading to subarachnoid hemorrhage with devastating consequences. Until now, the exact etiology of intracranial aneurysms formation remains unclear. The low incidence of subarachnoid hemorrhage in comparison with the prevalence of unruptured IAs suggests that the vast majority of intracranial aneurysms do not rupture and that identifying those at highest risk is important in defining the optimal management. The most important factors predicting rupture are aneurysm size and site. In addition to ambiental factors (smoking, excessive alcohol consumption and hypertension), epidemiological studies have demonstrated a familiar influence contributing to the pathogenesis of intracranial aneurysms, with increased frequency in first- and second-degree relatives of people with subarachnoid hemorrhage. In comparison to sporadic aneurysms, familial aneurysms tend to be larger, more often located at the middle cerebral artery, and more likely to be multiple. Other than familiar occurrence, there are several heritable conditions associated with intracranial aneurysm formation, including autosomal dominant polycystic kidney disease, neurofibromatosis type I, Marfan syndrome, multiple endocrine neoplasia type I, pseudoxanthoma elasticum, hereditary hemorrhagic telangiectasia, and Ehlers-Danlos syndrome type II and IV. The familial occurrence and the association with heritable conditions indicate that genetic factors may play a role in the development of intracranial aneurysms. Genome-wide linkage studies in families and sib pairs with intracranial aneurysms have identified several loci on chromosomes showing suggestive evidence of linkage, particularly on chromosomes 1p34.3-p36.13, 7q11, 19q13.3, and Xp22. For the loci on 1p34.3-p36.13 and 7q11, a moderate positive association with positional candidate genes has been demonstrated (perlecan gene, elastin gene, collagen type 1 A2 gene). Moreover, 3 of the polymorphisms analyzed in 2 genes (endothelial nitric oxide synthase T786C, interleukin-6 G572C, and interleukin-6 G174C) were found to be significantly associated with ruptured/unruptured aneurysms: the endothelial nitric oxide synthase gene single-nucleotide polymorphisms increased the risk, while IL-6 G174C seemed protective. More recently, two genomic loci (endothelin receptor A and cyclin-dependent kinase inhibitor 2BAS) have been found to be significantly associated with intracranial aneurysms in the Japanese population; endothelin-1 is a potent vasoconstrictor produced by the endothelial cells. Until now, there are no diagnostic tests for specific genetic risk factors to identify patients who are at a high risk of developing intracranial aneurysms. Knowledge of the genetic determinants may be useful in order to allow clues on stopping aneurysm formation and obtain diagnostic tools for identifying individuals at increased risk. Further multicenter studies have to be carried out.

Immune cell populations decrease during craniotomy under general anesthesia

BACKGROUND

Postoperative infections are common and potentially fatal complications in neurosurgical intensive care medicine. An impairment of immune function after central nervous system surgery is associated with higher risk of infection and postoperative complications. The aim of our study was to investigate how the immune cell population changes during the anesthesia process in patients undergoing craniotomy surgery.

METHODS

Patients undergoing craniotomy who had an inhaled general anesthetic were studied. Blood samples were collected before anesthesia and 30, 45, 60, 120, and 240 minutes after anesthesia began. Blood counts for neutrophils, monocytes, and lymphocytes were determined along with lymphocyte subpopulations (T cells, inducer and helper T cells, suppressor and cytotoxic T cells, natural killer cells, and B cells). Plasma concentrations of interleukin (IL)-2, IL-4, IL-6, and IL-10 were also measured along with tumor necrosis factor-α and interferon-γ. Data were analyzed by SPSS 13.0 software using repeated-measures analysis of variance followed by a Bonferroni correction.

RESULTS

Eighteen patients were enrolled in this study. In the comparison of the immune cell counts during neuroanesthesia, we found that at 30 minutes after anesthesia induction, neutrophils, monocytes, and lymphocytes decreased 18% (95% confidence interval [CI]: 11.0%-24.6%), 34% (95% CI: 16.2%-51.1%), and 39% (95% CI: 29.0%-48.9%) compared with their levels before anesthesia. At extubation the neutrophils returned to the base level. It also showed that natural killer cells decreased significantly during anesthesia. The concentration of cytokines in peripheral blood did not change significantly.

CONCLUSION

Our results showed that anesthesia and surgery upset the balance of the immune system during craniotomy, and a significant decrease in immune cell populations emerged after induction under general anesthesia.

The genetics of sporadic ruptured and unruptured intracranial aneurysms: a genetic meta-analysis of 8 genes and 13 polymorphisms in approximately 20,000 individuals

Object

Intracranial aneurysms (IAs) are thought to have a multifactorial origin. The authors undertook a comprehensive meta-analysis on all genes investigated using a case-control model in ruptured (subarachnoid hemorrhage) and unruptured aneurysms.

Methods

Electronic databases were searched until and including July 2008 for any candidate gene studied in IA or subarachnoid hemorrhage using a case-control model. The ORs and 95% CIs were determined for each gene-disease association using fixed and random effect models.

Results

Thirty studies of 8 genes and 13 polymorphisms were analyzed among 19,961 individuals (6622 cases and 13,339 controls). Two genes and 3 polymorphisms were associated with IA. The eNOS gene T786C polymorphism (OR 1.24, 95% CI 1.0–1.54; p = 0.05) and IL-6 gene G572C polymorphism (OR 7.08, 95% CI 2.85–17.57; p < 0.0001) both showed a significant association with ruptured/unruptured IA. The IL-6/G174C polymorphism exerted a significant protective effect against IA (OR 0.49, 95% CI 0.25–0.95; p = 0.04). The other candidate genes investigated (ACE, endoglin, APOE, elastin, MMP-3, and SERPINA3) showed no significant associations.

Conclusions

There is a likely genetic basis to sporadic IAs. However, the evidence base is small when compared against other complex disorders.

Potential Role of Thymosin-alpha1 Adjuvant Therapy for Glioblastoma

Glioblastomas are high-grade, malignant CNS neoplasms that are nearly always fatal within 12 months of diagnosis. Immunotherapy using proinflammatory cytokines such as IL-2 or IL-12 may prolong survival with glioblastoma. Thymosin-α1 (Talpha1) is a thymic hormone and immunemodulator that increase IL-2 production and T-cell proliferation. We examined potential therapeutic effects of Talpha1 in experimental in vivo glioblastoma, and characterized Talpha1's anti-tumor effects in vitro. Rar 9L cells (10⁴) were implanted into the right frontal lobe of adult Long Evans rats that were subsequently treated with vehicle, BCNU, Talpha1, or Talpha1+BCNU from postoperative day 6. Talpha1+BCNU significantly lowered tumor burdens, and increased cure rates. In vitro experiments demonstrated that Talpha1 had no direct effect on viability or mitochondrial function, and instead, it increased expression of pro-apoptosis genes, including FasL, FasR and TNFα-R1 (65.89%, 44.08%, and 22.18%, resp.), and increased 9L cell sensitivity to oxidative stress. Moreover, Talpha1 enhanced 9L cell sensitivity to both Granzyme B- and BCNU-mediated killing. The findings suggest that Talpha1 enhances BCNUmediated eradication of glioblastoma in vivo, and that Talpha1 mediates its effects by activating pro-apoptosis mechanisms, rendering neoplastic cells more sensitive to oxidative stress and immune-mediated killing by Granzyme B and chemotherapeutic agents.

Early prediction of infection after craniotomy for brain tumours

Reliably predicting infection soon after craniotomies would prevent infection and reduce treatment costs and hospitalization expenses. Therefore we analysed potential risk factors and blood count data after craniotomies for brain tumours in order to predict infection as soon as possible after surgery. We analysed 139 patients who underwent craniotomies for brain tumours from January 1997 to December 2001, and divided them into four categories (Types A to D) according to the following: increase in their white blood counts (WBCs) from Day 0 to Day 1, maximum WBC between Day 0 and Day 2, and maximum c-reactive protein (CRP) between Day 0 and Day 4 after surgery. We evaluated potential risk factors and the blood count data for infections via logistic regression analysis. Type D patients had a significantly higher rate of infection (p = 0.0123) than the other Types, while Type B patients had the lowest rate among the four groups (p = 0.0006). When Type A patients suffered CSF leakages, they had a significantly higher possibility of meningitis (p < 0.0001) or scalp infection (p = 0.012). In those Type A or D patients who were male, more than 70 years old, and suffered from metastases from primary lung cancer lesions, the possibility of pneumonia was significantly higher (p = 0.0178). In conclusion, we are able to predict infection within four days after craniotomies for brain tumours according to standard blood count data and certain risk factors. This possibility allows for improved care and better clinical outcomes in patients that undergo craniotomies for brain tumours.

Comparison of shunt infection incidence in high-risk subgroups receiving antibiotic-impregnated versus standard shunts

BACKGROUND

Shunt infection is a morbid complication of CSF shunting. Though antibiotic-impregnated shunt (AIS) systems decrease shunt infections by preventing bacterial colonization following device implantation, their effectiveness in populations at high risk for infection has recently been disputed. We set out to determine whether the categorical switch to AIS systems at our institution has resulted in a decreased incidence of shunt infection in high-risk pediatric patients.

METHODS

We retrospectively reviewed the records from all pediatric patients undergoing CSF shunt procedures at The Johns Hopkins Hospital over a 10-year period between January 1997 and December 2007. During the 5.75 years prior to October 2002, all CSF shunts included standard, non-AIS catheters. During the 4.25 years after October 2002, all CSF shunts included AIS catheters. High-risk subgroups were defined a priori as prematurity (<35 weeks gestational age), shunts placed immediately post-meningitis, conversion of external ventricular drains (EVD) to shunt, and replacement of nosocomial shunt infection in patients requiring prolonged hospital stay (>1 month).

RESULTS

A total of 544 pediatric patients underwent 1,072 shunt placement procedures (502 AIS, 570 non-AIS). Of patients with non-AIS catheters, 64 (11.2%) experienced shunt infection, whereas only 16 (3.2%) patients with AIS catheters experienced shunt infection (p<0.001). AIS versus non-AIS was associated with decreased shunt infection in premature neonates [three (5.5%) vs. seven (20.0%), p=0.030], acutely following bacterial meningitis [two (5.7%) vs. nine (25.0%), p=0.043], when converting EVD to shunts [zero (0%) vs. four (13.3%), p=0.030], and in patients with prolonged hospital stay>1 month [three (5.3%) vs. 12 (18.5%), p=0.022]. Staphylococcus aureus was the most common infectious agent for both non-AIS (81.3%) and AIS (75.0%) systems.

CONCLUSION

The introduction of AIS catheters into our institutional practice has reduced the incidence of shunt infection in pediatric populations at highest risk for infection. AIS catheters are effective instruments to prevent peri-operative colonization of CSF shunt components.

The interleukin-6 gene -174G>C and -572G>C promoter polymorphisms are related to cerebral aneurysms

BACKGROUND AND AIMS

An important part is played by inflammation in intracranial aneurysm formation. The hypothesis that there is an association of the proinflammatory cytokine interleukin-6 (IL-6) genotypes (-572G>C and -174G>C) with intracranial aneurysms was tested.

METHODS

IL-6 genotypes were determined in 91 Caucasian patients with aneurysms and compared with 2720 healthy UK controls.

RESULTS

For both polymorphisms, the distribution of the genotypes and estimated allele frequency were different between the control group and the aneurysm group. For -572G>C, a higher frequency of the C allele (p = 0.001) and more people homozygous for the C allele were found among those with aneurysms than among the controls (4.4% v 0.3%, p = 0.001). For -174G>C, more people homozygous for the C allele were found among the controls than among those with aneurysm (18% v 7%, p = 0.007). The 572C/174G haplotype was associated with an increased risk of aneurysms, with the relative risk compared with the common haplotype being 1.89 and that for the -572G/174C haplotype being 0.58 (p<0.0005).

CONCLUSION

This is the first study to show that IL-6 promoter polymorphisms are associated with intracranial aneurysmal disease. Whether this association is with the development, progression or rupture of such aneurysms, or represents survivor bias, is unclear.

Increased concentrations of transforming growth factor β1 and β2 in the plasma of patients with glioblastoma

Recently, several in vitro studies have demonstrated production of the potent immunosuppressive cytokine transforming growth factor beta (TGF-beta)2 in glioblastoma cell lines. Systematic studies of the concentration of TGF-beta isoforms in the plasma of patients harboring intracerebral tumors do not exist. In the present study, the concentrations of TGF-beta1 and TGF-beta2 in platelet-poor plasma of 21 patients with glioblastoma before and after extensive resection were measured by specific ELISA systems and related to survival. The plasma concentrations of latent TGF-beta1 of patients with glioblastoma prior to surgery were significantly higher in comparison to healthy control probands, but not to patients with multiple sclerosis (MS). Furthermore, latent TGF-beta2 was found to be significantly increased in the plasma of patients with glioblastoma in comparison to healthy control probands and patients with MS. After extensive resection of the tumor, the value of latent TGF-beta2 evidently decreased. Interestingly, the concentration of latent TGF-beta2 prior to surgery was correlated with survival and a strong relationship was found between the survival and the difference of latent TGF-beta2 levels prior to surgery minus the TGF-beta2 concentrations 7 days after surgery. A higher difference in these plasma concentrations >6 ng/ml vs. <6 ng/ml clearly correlates with a longer survival time. In conclusion, this study suggests that glioblastoma does secret TGF-beta2 in vivo and that TGF-beta2 may play an important role in glioblastoma patients.

Nosocomial infections in neurosurgery intensive care units

BACKGROUND

Nosocomial infections can lead to complications in the patients admitted to neurosurgery intensive care units. The most common causes are ventriculitis, shunt infections, meningitis, surgical wound infections, urinary tract infections, pneumonia, intravascular catheter related to infections and gastrointestinal infections.

AIM AND OBJECTIVE

This article is written to determine strategies that nurses can apply to minimize nosocomial infections seen in neurosurgery intensive care units.

DESIGN

The article is systematic review.

METHOD

A MEDLINE and CINAHL search was carried out using descriptor terms. This overview is targeted at neurosurgery intensive care nurses to demonstrate to them that principles of infection control in the neurosurgery intensive care units are based on simple concepts and that basic measures are easy to implement at the bedside. The 20 articles were identified that met the requirements for methodological quality and inclusion criteria.

RESULT

In order to reduce infection rates it is useful to inform intensive care nurses about the infection sources and it is useful to change their behaviours.

CONCLUSION

Infection control measures are to be viewed as priority and have to be integrated fully into the continuous process of improvement of quality of care.

RELEVANCE TO CLINICAL PRACTICE

Little research about the treatment/care and rates of nosocomial infections in the neurosurgery care unit was found. It was found that this subject has not been widely covered in nursing journals. This article can provide knowledge regarding the effective strategies of infection control in the neurosurgery intensive care units. Practicing nurses can use that knowledge to enhance the quality of nursing care.

Type 1/Type 2 immunity in infectious diseases

T helper type 1 (Th1) lymphocytes secrete secrete interleukin (IL)-2, interferon-gamma, and lymphotoxin-alpha and stimulate type 1 immunity, which is characterized by intense phagocytic activity. Conversely, Th2 cells secrete IL-4, IL-5, IL-9, IL-10, and IL-13 and stimulate type 2 immunity, which is characterized by high antibody titers. Type 1 and type 2 immunity are not strictly synonymous with cell-mediated and humoral immunity, because Th1 cells also stimulate moderate levels of antibody production, whereas Th2 cells actively suppress phagocytosis. For most infections, save those caused by large eukaryotic pathogens, type 1 immunity is protective, whereas type 2 responses assist with the resolution of cell-mediated inflammation. Severe systemic stress, immunosuppression, or overwhelming microbial inoculation causes the immune system to mount a type 2 response to an infection normally controlled by type 1 immunity. In such cases, administration of antimicrobial chemotherapy and exogenous cytokines restores systemic balance, which allows successful immune responses to clear the infection.