Microstress, mood, and natural killer-cell activity

The interactions between transient minor negative and positive life events ("microstressors"), concurrent mood states, and immunological functioning were assessed by measuring levels of natural killer-cell activity (NKA), stress, and mood weekly for four weeks. No association was found between the frequency of either positive or negative microstressors and NKA, nor between concurrent mood ratings and NKA. Some individuals showed a marked and unexplained variability in NKA on a week-to-week basis. These results do not support the hypothesis that the minor stresses of everyday living affect immune function. The study does suggest that single cross-sectional determinations of NKA may not be suitable for studies of psychosocial factors and NKA.     

Immunological consequence of renal transplantation and immunosuppression. I. Alterations in human natural killer-cell activity

The role and activity of natural killer (NK) cells following renal transplantation remain unknown. To monitor NK activity, a⁵¹Cr release of K-562 targets in prednisone-and azathioprine-treated patients receiving renal allografts was utilized. In 18 patients in whom NK activity was measured prior to and after transplantation, a significant diminution in NK activity within 3 weeks following transplantation was demonstrated compared to pretransplant values (34.71 vs 12.20%, respectively;P<0.001). In 11 subjects who had NK activity assayed at various intervals after transplantation but not prior to allografting, mean NK values were markedly lower (mean, 14.2%) than those of normal volunteers or patients maintained on hemodialysis (P<0.001). The latter two control groups demonstrated no difference (P = NS) in mean NK activity (39.46 vs 35.82%, respectively). In 5 of the 29 patients evaluated with good long-term graft function (mean, 2.7 years), restitution of normal NK activity was demonstrated. In two patients with bacterial infections, NK activity increased from 39.29 to 51.7% and from 13.54 to 20.00%. After infection, these values were 35.3% in the former and 3.39% in the latter. Viral infection did not appear to affect NK activity significantly. NK activity was increased in only one of seven patients with documented rejection episodes. In three of such patients, NK activity declined significantly following pulse methylprednisolone therapy. These results indicate that (1) NK-cell activity significantly decreases immediately after transplantation, probably as a result of immunosuppressive therapy; (2) NK activity does not appear to be stimulated by the alloreactive rejection process; (3) NK activity may be augmented in the course of bacterial but not viral infections; and (4) long-term allograft survival may be associated with a restoration of NK-cell levels in certain recipients.     

The biology of human natural killer-cell subsets.

Human natural killer (NK) cells comprise approximately 15% of all circulating lymphocytes. Owing to their early production of cytokines and chemokines, and ability to lyse target cells without prior sensitization, NK cells are crucial components of the innate immune system. Human NK cells can be divided into two subsets based on their cell-surface density of CD56--CD56(bright) and CD56(dim)--each with distinct phenotypic properties. Now, there is ample evidence to suggest that these NK-cell subsets have unique functional attributes and, therefore, distinct roles in the human immune response. The CD56(dim) NK-cell subset is more naturally cytotoxic and expresses higher levels of Ig-like NK receptors and FCgamma receptor III (CD16) than the CD56(bright) NK-cell subset. By contrast, the CD56(bright) subset has the capacity to produce abundant cytokines following activation of monocytes, but has low natural cytotoxicity and is CD16(dim) or CD16(-). In addition, we will discuss other cell-surface receptors expressed differentially by human NK-cell subsets and the distinct functional properties of these subsets.     

The effect of acute exercise on natural killer-cell activity of trained and sedentary human subjects

The effect of acute exercise on natural killer (NK) activity and on the distribution of phenotypic characteristics of peripheral blood lymphocytes was examined. Trained and sedentary individuals underwent a standard progressive exercise test on a cycle ergometer using an incremental work load of 15 W (90 kpm), increased every minute. Each subject was encouraged to exercise to exhaustion, and total ventilation and mixed expired O₂ and CO₂ were measured every 30 sec. All subjects reached the anaerobic threshold as judged by the deflection of ventilation at a work load nearVO_2max. NK activity against K562 reached maximum levels immediately after exercise, dropped to a low point 120 min later, then slowly came back to preexercise levels within 20 hr. No significant differences were observed between the trained and the sedentary groups. Furthermore, immediately after exercise the proportion of OKT-3+ and OKT-4+ cells was reduced by 29.8±3.6 and 33.6±5.4%, respectively; the percentage Leu-7+ and Leu-11a+ cells was increased by 53.9±1.7 and 57.3±2.9%, respectively. The percentage OKT-8+ cells was not significantly altered. When the percentage binding of effector to target cells was examined, it was highest at 0 min post-exercise (19±6.2%) and lowest at 120 min postexercise (7±3.9%), but the absolute number of NK cells remained unchanged. The source of serum used in the lytic assay had no effect on the NK activity, as fetal calf serum and autologous sera drawn at different time intervals during exercise gave similar results. Epinephrine suppressed and interferon enhanced the NK activity of all cells tested, which indicates that during and after exercise NK cells did not go through a refractory stage. Our results show that, contrary to other lymphocyte subpopulations, NK cells are resistant to the depletive and modulatory effects of acute exercise and the increase in NK activity is not due to an increase in the absolute number of NK cells.     

Large granular lymphocyte proliferation with the natural killer-cell phenotype.

Lymphoproliferated disorders involving large granular lymphocytes (LGL) can be divided into a common T-cell subset (CD3+, CD8+) and a rarer natural killer (NK)-cell subset (CD2+, CD3-). The immunophenotype, clinical pathologic features, and cytogenetic and molecular genetic analyses are reported for seven patients with NK-cell-LGL proliferation. The typical immunophenotype was CD2+, CD3-, CD4-, CD11b+, and CD16+ or CD56+. A low but variable percentage of cells were CD8+ or CD57+. Unusual phenotypes with CD2- (1 of 7), CD11b- (1 of 7), or CD16-/CD56- (1 of 7) cells were seen. Strong NK-cell activity was observed in all cases, indicating that none of the NK-cell markers (CD11b, CD16, CD56, CD57) is essential for NK-cell activity. One patient died shortly after diagnosis from coexistent refractory multiple myeloma and another patient died within 1 month from the LGL proliferation. The other patients had been followed for 12 to 70 months, with a median follow-up period of 38 months. There was no progression of their LGL proliferation. Lymphocyte counts varied from 3.3 x 10(3)/microL to 58.4 x 10(3)/microL at the time of diagnosis. Unexplained anemia and neutropenia were observed in one patient. Cytogenetic abnormalities were detected in two of four patients studied with t(6;12) in one and der(5), der(6), and der(11) in the other. The approximately T gamma and T beta genes were in the germline configuration and Epstein-Barr virus DNA was undetectable in five of five patients studied. Natural killer-cell LGL proliferations were morphologically indistinguishable from T-cell LGL proliferations. However, the two were immunophenotypically and genotypically distinct and NK-cell activity was consistently observed in the former. Most of the NK-cell proliferations also were chronic indolent disorders and the incidence of associated cytopenias seemed to be lower than T-cell LGL proliferations.     

Ultrastructural effects of dietary galactoflavin on mouse hepatocytes

The ultrastructural effects of a galactoflavin-supplemented, riboflavin-free diet were chronologically examined in mouse hepatocytes. The mitochondrial population suffered the greatest changes. Beginning with day 3 of the experimental diet, the mitochondria first became elongated, then later rounded up to become somewhat enlarged spheres. By day 20–22, the mitochondria reached diameters of about 6 μm, and had cristae that were largely confined to the periphery of the organelles. Throughout the course of enlargement, spontaneously partitioned mitochondria of all sizes were common. When mice with advanced ariboflavinosis were injected with riboflavin, mitochondrial recovery took place over a period of more than 10 days. Division of the enlarged mitochondria proceeded by medial attenuation, rather than by partition formation and constriction. The mechanism that selects which of the two modalities of mitochondrial replication will prevail remains undetermined.     

Inhibition of mouse natural killer activity by cyclosporin A.

Cyclosporin A(CSA), administered in vivo or in vitro, inhibited the spontaneous cytotoxicity of C57BL/6 and NZB/WF1 mouse spleen cells against YAC and K562 target cells in a 4 hr 51Cr release assay. Inhibition of natural killing (NK) by CSA occurred rapidly, was dose-dependent, and did not require the presence of T cells, B cells or macrophages. CSA depressed NK activity by direct interaction with NK cells. There was no evidence that inhibition of NK by CSA was mediated through suppressor cells.     

Transmembrane T-cell receptor peptides inhibit B- and natural killer-cell function

A synthetic hydrophobic peptide (core peptide; CP) containing two positively charged amino acids, lysine and arginine was derived from the transmembrane sequence of the T-cell receptor (TCR) alpha chain and has been shown to inhibit T-cell-mediated inflammation. In this study, we investigated the specificity of CP (10 microm) on lymphocyte function and found that it significantly inhibited interleukin-2 production in T cells and natural killer cytotoxicity by 46-58% compared to positive control. CP had no effects on B-cell proliferative responses when used at these concentrations; however, it suppressed B-cell proliferation at higher concentrations (50 microm). Inhibition by CP was not the result of membrane pore formation or cytotoxicity when examined by trypan blue, propidium iodide staining or transmission electron microscopy. CP analogues, with both lysine and arginine replaced by neutral or negatively charged amino acids, or by randomly distributing charges in the peptide sequence, had no effect on lymphocyte function. These results suggest that peptide inhibition is affected by its structure and charge interactions, and may involve common signalling molecules in T, B and natural killer cells. The potential of the immuno-inhibitory effects of CP as a novel anti-inflammatory peptide in therapy should be further explored.     

The effect of 6-mercaptopurine on natural killer-cell activities in Crohn's disease

Crohn's disease patients on long-term 6-mercaptopurine therapy (more than 4 months) were evaluated for activity of peripheral blood natural killer cells. Natural killer-cell cytolytic activity against K-562 tumor-cell targets was examined, as was natural killer-cell suppression of lymphoblastoid B-cell antibody production. In addition, these patients were studied for their ability to generate antitetanus-specific IgG antibody-producing lymphoblastoid B cells followingin vivo booster immunization. Crohn's disease patients on 6-mercaptopurine therapy had significant reductions in peripheral blood natural killer-cell activity against K-562 targets compared to normals, disease controls, and Crohn's disease patients not on 6-mercaptopurine. Natural killer-cell suppression of lymphoblastoid B-cell antibody production was like-wise decreased in 6-mercaptopurine-treated patients compared to normal controls. In contrast, thein vivo generated lymphoblastoid B-cell antibody responses of Crohn's disease patients on 6-mercaptopurine therapy were not decreased compared to normal, while Crohn's disease patients not on 6-mercaptopurine therapy had significantly impaired IgG antitetanus antibody responses. These findings suggest that 6-mercaptopurine therapy in Crohn's disease affects several lymphoid subpopulations, resulting in a decreased natural killer-cell cytotoxic activity against K-562 target cells and a decreased natural killer-cell ability to suppress lymphoblastoid B-cell antibody production, as well as an improved humoral immune response following tetanus toxoid booster immunization.     

Mechanism of stimulation of natural killer-cell cytotoxicity by interferon and an interferon-inducer in the rat.

The interferon-induced Newcastle disease virus (NDV) was shown to augment cytotoxicity attributable to natural killer (NK) cells in all of the major lymphoid organs of W/Fu rats except the thymus. The levels of interferon isolated from the spleen following NDV inoculation correlated with the increase in splenic cytotoxicity from the same spleen. Spleen-derived interferon was shown to augment splenic cytotoxicity following intravenous inoculation, and to augment spleen cell cytotoxicity in vitro. Three major peaks of interferon type I were found in spleen homogenates corresponding to mol. wt of greater than 100,000, 29-33,000 and 19-23,000. All these fractions stimulated spleen cell cytotoxicity when tested in vitro. The rapid drop in splenic cytotoxicity 24 hr after NDV inoculation was associated with a rapid fall in interferon levels in vivo. The need for the continued presence of interferon for the stimulation of cytotoxicity was demonstrated when spleen cells pretreated with interferon for 4 hr in vitro lost their augmented cytotoxicity upon culturing for a further 20 hr in the absence of interferon. Although splenic cytotoxicity returned to control levels within 24 hr of a single 10(7.3) EID50 dose of NDV, repeated doses of NDV maintained augmented cytotoxicity over a longer period. Spleen cells either taken from rats injected with NDV or pretreated in vitro with interferon showed a two-fold increase in the number of cytotoxic cells bound to W/FuG-1 target cells, with no change in the target binding-cell numbers. However, only the cells pretreated with interferon showed an increase in lytic efficiency.     

Suppression of natural killer-cell function in humans following thermal and traumatic injury

Depressed cell-mediated and humoral immune functions have been reported to occur following severe thermal and traumatic injury. In this study we have questioned whether another immune function, natural killing (NK), is also disturbed in these injured patients. Twenty-two thermally injured patients with burns ranging from 5 to 75% of the total body surface area and 15 traumatically injured patients with injury severity scores ranging from 9 to 56 were followed postinjury and compared to 29 age-matched controls. NK activity was measured as the percentage cytotoxicity in chromium-51 release assays with K562 target cells. The more severely burned patients had significantly depressed NK activity for the 40-day period following injury that remained reduced for the duration of the study. Patients with lesser burns had reduced NK-cell function for the initial 10-day period postburn that returned slowly to the normal range. Traumatically injured patients had depressed NK-cell function during the 3- to 6-day period postinjury. The percentage of cells bearing phenotypic markers for the groups in which Nk cells are found was either normal or elevated in these patients. A correlation was found between NK activity and interleukin 2 generation by mononuclear cells from these patients. In order to investigate the mechanism of NK suppression in these patients, NK-cell function was studied following the infusion of cortisol, epinephrine, and glucagon into volunteer subjects in amounts known to reproduce serum levels seen following injury of moderate severity. NK-cell function was reduced an average of 66% following infusion, suggesting that the inhibition of NK-cell function seen in patients may be mediated by the stress response to injury.     

Differential effects of sucrose and fructose on dietary obesity in four mouse strains

We examined sugar-induced obesity in mouse strains polymorphic for Tas1r3, a gene that codes for the T1R3 sugar taste receptor. The T1R3 receptor in the FVB and B6 strains has a higher affinity for sugars than that in the AKR and 129P3 strains. In Experiment 1, mice had 40 days of access to lab chow plus water, sucrose (10 or 34%), or fructose (10 or 34%) solutions. The strains consumed more of the sucrose than isocaloric fructose solutions. The pattern of strain differences in caloric intake from the 10% sugar solutions was FVB > 129P3 = B6 > AKR; and that from the 34% sugar solutions was FVB > 129P3 > B6 ≥ AKR. Despite consuming more sugar calories, the FVB mice resisted obesity altogether. The AKR and 129P3 mice became obese exclusively on the 34% sucrose diet, while the B6 mice did so on the 34% sucrose and 34% fructose diets. In Experiment 2, we compared total caloric intake from diets containing chow versus chow plus 34% sucrose. All strains consumed between 11 and 25% more calories from the sucrose-supplemented diet. In Experiment 3, we compared the oral acceptability of the sucrose and fructose solutions, using lick tests. All strains licked more avidly for the 10% sucrose solutions. The results indicate that in mice (a) Tas1r3 genotype does not predict sugar-induced hyperphagia or obesity; (b) sucrose solutions stimulate higher daily intakes than isocaloric fructose solutions; and (c) susceptibility to sugar-induced obesity varies with strain, sugar concentration and sugar type.     

Human natural killer-like activity against mouse spleen cells

Unstimulated human peripheral lymphocytes were cytotoxic for normal mouse spleen cells and suppressed the in vitro antibody plaque-forming cell (PFC) response of these cells to sheep red blood cells and dinitrophenylated Ficoll. The cells in the lymphocyte population that were responsible for the immunosuppression had properties of natural killer (NK) or NK-like cells in that they were: (a) non-E-rosetting, (b) nonadherent, (c) unaffected by treatment with anti-human immunoglobulin plus complement, (d) cytotoxic against an established human NK target, K562 leukemic cells, and (e) partially inactivated by mitomycin C. Addition of the human NK-like cells to mouse spleen cell cultures at the time of antigen addition and at an effector cell to target cell ratio as low as 0.67:1 resulted in 85 to 96% suppression of the PFC response. Addition of NK-like cells to cultures 18 h before harvesting in 5-day cultures required higher concentrations and ratios (2.7 : 1) of effector to target cells to significantly suppress the PFC response. The data suggest that human NK-like activity in suppression of the mouse PFC response is due to killing of the targets. The mouse spleen cell PFC system represents a potential model for assessment of human NK activity that is quite dramatic in its effect and can be used in addition to the well known ⁵¹Cr-release assay. Also, since the mouse spleen cell is a normal cell, it provides a model in the PFC system for studying the mechanism of NK regulation of normal cellular function. An additional finding of this study was the observation that E-rosetting T cells significanty enhanced the mouse PFC response. Thus, human peripheral lymphocytes contain discrete cellular populations that either enhance or suppress the mouse PFC response.     

Impaired neonatal natural killer-cell activity to herpes simplex virus: Decreased inhibition of viral replication and altered response to lymphokines

Human adult natural killer (NK) cells were recently demonstrated to inhibit herpes simplex virus (HSV) replicationin vitro. In this study we compared the ability of newborn and adult NK cells to inhibit HSV replication. Cord blood mononuclear cells (MNCs) from healthy, term newborns and MNCs from adults were analyzed for their percentage of Leu-11⁺ cells and comparedin vitro for their NK-cell activity against HSV-infected fibroblasts and the tumor cell line K562. Cord blood MNCs, compared with adult MNCs, had significantly lower percentages of Leu-11⁺ cells (5 vs 11%;P<0.01), less anti-K562 NK activity (6 vs 54 lytic units/10⁷ cells;P<0.001), and less anti-HSV NK activity (5 vs 52% HSV plaque inhibition;P<0.02). Comparing individual neonates and adults with equal percentages of Leu-11⁺ cells, neonatal MNCs still had less NK activity against either target. When Leu-11⁺ MNCs were isolated using the fluorescence-activated cell sorter, neonatal Leu-11⁺ MNCs still inhibited HSV replication less than adult Leu-11⁺ MNCs (P<0.01). MNCs from some neonates had significant anti-K562 NK activity but poor anti-HSV NK activity, suggesting either nonidentical NK-cell subpopulations or specific suppression. Whereas neonatal NK activity against K562 was always augmented by prior exposure to either interferon (IFN) or interleukin-2 (IL-2), the neonatal NK activity against HSV-infected cells was only augmented for half of the neonates tested. Endogenous production of alpha-IFN and gamma-IFN by MNCs exposed to HSV-infected fibroblasts was the same for cells from neonates or from HSV-seronegative adults. More gamma-IFN was produced by MNCs from HSV-seropositive adults than from neonates or HSV-seronegative adults. These results suggest that although newborns have phenotypically identifiable NK cells and the capacity for IFN production, the ability of the NK cells to inhibit HSV replication is impaired, and their level of response and augmentation by specific lymphokines is target specific.     

Mental activity and the e.e.g.: Task and workload related effects

The e.e.g. was recorded from the left and right parietal and temporal regions of the scalps of 23 normal subjects while they were mentally at rest and then while they were executing tasks intended to engage, firstly, their dominant cerebral hemispheres, and secondly then their nondominant hemispheres. In each of the alpha and gamma frequency bands, 43 features of the e.e.g. expressed in terms of average power densities, coefficients of power density variation, coherencies and phases were calculated for each of the subjects. A method of separating the features which were related to the nature of the mental task from those which were related only to the mental workload represented by each of the tasks is presented. Of the features considered, many were found to be workload related, but only five, namely a power density variance, a right to left power ratio, an anterior to posterior phase angle and two coherency ratios, showed task-dependent behaviour. In this latter group, only two features point to the lateralisation of verbal and spatial cognitive processes to the dominant and nondominant cerebral hemispheres. The problem of the confounding of cerebral and mygenic effects and possible bias in the results owing to this effect is discussed.     

Impact of changes in housing condition on mouse natural killer cell activity

Various psychosocial stressors, such as housing condition and rotation, have been reported to influence tumour growth. This study assessed the influence of housing condition and change in housing condition on natural killer (NK) cell activity, an important component of natural immune defense against cancer. Mice which were individually housed for four weeks did not differ from group-housed mice in NK cell cytolytic activity against tumour targets in vitro or in the frequency of NK cells in the spleen. Switching of housing condition (group to individual, individual to group) for one week did not change the splenic NK cytolytic capacity relative to mice which were not switched. The two groups of mice which experienced a change in housing condition were, however, significantly different from each other. These data suggest that an acute change in housing condition, rather than the housing condition per se, has differential effects on the capacity to kill tumours by NK cells.     

Expression of p53 protein in T- and natural killer-cell lymphomas is associated with some clinicopathologic entities but rarely related to p53 mutations

To determine if p53 abnormalities could be involved in the pathogenesis of T- or natural killer (NK)-cell lymphomas, we investigated 51 cases of these lymphomas for the expression of p53 and its relationship with p53 gene mutations, the expression of the p21 protein as well as the proliferative and apoptotic indices. Overexpression of p53 was found in 19 cases (37%), whereas mutations of the p53 gene were observed in only 5 of 28 tested cases. The analysis of immunohistochemical data showed some entity-related phenotypic profiles. Anaplastic large cell lymphomas showed a frequent overexpression of p53 (7/8 cases) and p21 (6/8 cases) proteins and rare p53 mutations (1/7 cases), suggesting accumulation of a functional wild type p53 protein able to induce p21 expression. Nodal peripheral T-cell lymphomas unspecified showed relatively frequent overexpression of p53 protein (5/7 cases), infrequent p21 expression (2/7 cases), and rare p53 gene mutations (1/6 cases). In angioimmunoblastic lymphomas, the common phenotype was p53-/p21- (15/17 cases), with only a few scattered p53-positive cells, which, on the basis of double staining results, were mostly Epstein-Barr virus-infected B cells. A p53 gene mutation was only found in 1 case (1/8 cases) of angioimmunoblastic lymphoma, which showed cytologic tumor progression. Mycosis fungoides showed p53 overexpression in 2 of 4 cases, including 1 case with p53 gene mutation and features of cytologic tumor progression. Nasal NK/T lymphomas showed p53 overexpression in 2 of 5 cases, 1 of which had a p53 gene mutation. Finally, all lymphoblastic T-cell lymphomas (5 cases) and gammadelta hepatosplenic T-cell lymphomas (3 cases) were negative for expression of p53 and p21 proteins. We conclude that p53 protein overexpression is a common finding in some entities of T- and T/NK-cell lymphomas, whereas a p53 gene mutation is a rare, sporadic, and rather late event associated with tumor progression in some instances. The p53/p21 expression pattern appears to be variable in T- and T/NK-cell lymphoma entities, reinforcing the concept of distinct, entity-related mechanisms of pathogenesis in these tumors.     

Analysis of natural killer effector and suppressor activity by intraepithelial lymphocytes from mouse small intestine.

Intraepithelial lymphocytes (IEL) are morphologically similar to NK cells in other tissues and we have studied the NK activity of IEL isolated from mouse small intestine. In contrast to spleen NK cells, IEL showed little activity against YAC-1 over 4 h but had high levels of NK activity when the assay was extended to 18 h. IEL from nude mice did not show the enhanced NK activity found in other tissues. IEL were also found to suppress the NK activity of spleen cells and this suppressor function was not mediated by T lymphocytes or macrophages. The results indicate that the intestinal epithelium contains a population of potent NK cells which may represent a type of NK cell different to that found in other tissues. In addition, there are also cells capable of regulating NK cell function in the epithelial layer.     

Failure of dietary restriction to influence natural killer activity in old rats

Natural killer activity of Sprague-Dawley rats maintained on an ad libitum versus restricted diet was compared using an 18 hour 51Cr-release assay, against the K562 erythroleukemic line, Yac-1 lymphoma cells and SV40-3T3 cells. The results indicated that no enhancement of natural killer function was induced by dietary restriction of 10.5-month-old rats from weaning. Prolongation of the restricted diet into late life (24 months) similarly did not enhance basal natural killer activity over levels observed in the ad libitum controls. This suggests that the improved resistance to some tumours seen after prolonged dietary restriction depends on another defensive mechanism, reduced metabolic activity and/or a reduction of available nutrients at cancerous foci.     

Intestinal T-cell and natural killer-cell lymphomas in Taiwan with special emphasis on 2 distinct cellular types: natural killer-like cytotoxic T cell and true natural killer cell

Primary intestinal lymphomas are rare, especially the T-cell and natural killer (NK)-cell types. Enteropathy-type T-cell lymphoma (ETL) is the most characteristic of the intestinal T-cell and NK-cell lymphomas (ITNKLs) defined in the World Health Organization classification. However, typical ETL is rare in nonendemic areas for celiac disease, which include Taiwan. With the exception of ETLs, ITNKLs comprise heterogeneous subtypes such as anaplastic large cell lymphoma, nasal-type NK/T-cell lymphoma and peripheral T-cell lymphoma, unspecified. Furthermore, the literature results with respect to the association between Epstein-Barr virus (EBV) and ITNKL are contradictory. To define the clinicopathological features of primary ITNKLs and develop a better understanding of their relationship with EBV in Taiwan, therefore, we investigated a sample of 11 patients based on the new World Health Organization classification using immunostaining, in situ hybridization for EBV detection, and polymerase chain reaction (PCR) for evaluation of T-cell receptor clonality. In conclusion, 2 distinct groups of primary ITNKLs were identified in our Taiwanese sample. The 6 group A cases were non-EBV-associated ETLs, prevalent in the jejunum and/or ileum. They were composed of monotonous round-ovoid medium-sized nuclei and had little pale cytoplasm. The immunophenotypes of these tumors were consistently CD3+, CD4-, CD8+, CD56+, T-cell intracellular antigen 1+, and Epstein-Barr early region- and monoclonal for T-cell receptor PCR, which indicated NK-like cytotoxic T-cell origin. The 5 group B cases were EBV-associated nasal-type NK/T-cell lymphomas prevalent in the ileum or cecum of younger patients. The neoplastic cells had polymorphous medium to large angulated nuclei and moderate cytoplasm, with immunologic phenotypes of CD4-, CD8-, variable cytoplasmic CD3varepsilon+, CD56+, T-cell intracellular antigen 1+, and Epstein-Barr early region 1+, and germ line PCR result for T-cell receptor, which indicated true NK-cell origin. The grave prognoses for the 2 groups did not differ significantly.