Monoclonal HNK-1 Research Articles

Natural killer cell activity in childhood acute lymphoblastic leukaemia in remission.

Fifteen children with acute lymphoblastic leukaemia (ALL) in remission receiving maintenance chemotherapy and 12 ALL patients off treatment and in remission were tested for natural killer (NK) cell activity in vitro. Compared with a control population the children with ALL receiving maintenance chemotherapy had low levels of NK cell activity. This effect was not due to a specific reduction in NK cell numbers since proportions of mononuclear cells detected by the monoclonal antibodies HNK-1 (Leu-7) and Leu-11a were normal. Furthermore NK cell activity in patients could only be partially increased by pre-incubation of effector cells with interferon (alpha IFN). These studies confirm the lack of NK cell activity in children with ALL and show that this phenomenon is directly related to functional NK cell impairment. Our study has further shown that this effect is transient since ALL patients off treatment and in remission showed normal levels and augmentation of NK cell activity.

Neural cell adhesion molecules and myelin-associated glycoprotein share a common carbohydrate moiety recognized by monoclonal antibodies L2 and HNK-1.

Cell surface molecules have been implicated in cell interactions which underlie formation of the nervous system. The analysis of the functional properties of such molecules has profited from the combined use of antibodies and cell culture systems. It has been suggested that the interplay between these molecules modulates cell-to-cell interaction at critical developmental stages. In the mouse, N-CAM and L1 antigen have been shown to mediate Ca2+-independent adhesion among neural cells. N-CAM plays a role in fasciculation of neurites and formation of neuromuscular junction. L1 is apparently not involved in synaptogenesis, but in migration of granule cell neurones in the developing mouse cerebellar cortex. The two antigens are distinct molecular and functional entities which act synergistically in aggregation of neuroblastoma and early postnatal cerebellar cells. In view of a certain similarity in function between the two groups of molecules, it was not surprising to find that structural similarities are detectable by the monoclonal antibody L2. We show here that a carbohydrate moiety recognized by L2 and HNK-1 monoclonal antibodies, is present in mouse N-CAM and L1. The L2 epitope appears on all major neural cell types but not all N-CAM molecules express it. This heterogeneity points to a previously undetected molecular diversity which may have functional implications for modulating cell adhesion during development.

Characterization of a subset of human natural killer cells that express OKM1 but lack HNK-1 (Leu-7) antigens.

The HNK-1(Leu-7) monoclonal antibody selectively identifies a population of human granular lymphocytes with natural killer (NK) cell activity. We previously reported that the HNK-1+ cell fraction purified from blood mononuclear cells accounted for virtually all NK activity in six individuals. In this study we analysed additional normal individuals and found that in eight out of 14 donors HNK-1+ cells, purified with a fluorescence-activated cell sorter (FACS), exhibited greatly enriched NK cell activity, whereas HNK-1- cells did not have significant activity. In four donors the HNK-1+ cells were enriched in NK activity compared with HNK-1- cells; however, the HNK-1- cells also had moderate levels of activity. In the two remaining donors, NK activity was not enriched in the HNK-1+ fraction in comparison with the HNK-1- fraction. To determine the cell type responsible for NK activity in the HNK-1- subset, these cells were further sorted with the FACS onto OKM1+ and OMK1- fractions and analysed for morphology and function. HNK-1- OKM1- cells were found to be small- to medium-sized lymphocytes devoid of NK activity in all donors tested, whereas most HNK-1- OKM1+ cells were granular lymphocytes and in some donors demonstrated NK function at a level comparable to HNK-1+ cells. Thus some individuals have an important subset of granular lymphocytes with NK-cell activity and the HNK-1- OKM1+ phenotype. It is important to account for these cells in studies involving granular lymphocytes and NK cell function.

A human lymphocyte antigen is shared with a group of glycoproteins in peripheral nerve

The monoclonal antibody HNK-1 binds to a carbohydrate determinant in the myelin-associated glycoprotein (MAG) and other glycoproteins of human peripheral nerve. Some glycoproteins of lower M r than the major P 0 glycoprotein of myelin appear to bind more antibody than MAG. These glycoproteins electrophorese in the M r range of 20,000 to 26,000 and are present in the purified myelin fraction. The results indicate that an antigen on the surface of a subset of lymphocytes is shared with a group of glycoproteins in human peripheral nerve. The antigen appears to be similar to that recognized by IgM paraproteins associated with a type of neuropathy.

The monoclonal antibody HNK-1 reacts with a human peripheral nerve ganglioside

The monoclonal HNK-1 antibody, a marker for human natural killer cells, strongly reacted with human peripheral nerve gangliosides in the enzyme-linked immunosorbent assay. Autoradiography after the binding of HNK-1 to thin-layer chromatograms of peripheral nerve gangliosides followed by radioiodinated goat anti-mouse IgM revealed that HNK-1 was reacting with a minor ganglioside that chromatographed between GM1 and GD1a. The antigen was insensitive to digestion with neuraminidase and pronase.

Identical reactivity of monoclonal antibodies HNK-1 and NC-1: conservation in vertebrates on cells derived from the neural primordium and on some leukocytes

NC-1 and HNK-1, two mouse monoclonal antibodies raised against quail ciliary ganglion and a human leukemic cell-line, respectively, were found to display the same pattern of reactivity. Species investigated included human, rodents, birds and amphibians. In 1- to 3-day-old avian embryos, migrating crest cells are stained, whereas in older animals neuroepithelial cells and neurons are labelled. Staining with fluorescein isothiocyanate-conjugated NC-1 is blocked by preincubation with HNK-1. In immunoblot analyses both antibodies recognize the same pattern of bands which are different in central and peripheral nervous systems and vary during development. Thus, HNK-1/NC-1 provides a useful tool for investigating the ontogeny of neural and lymphocytic cells carrying this determinant, which, in view of its high degree of conservation during vertebrate evolution, may play an important part within the haematopoietic and nervous systems.

Interferon-α regulation of lymphocyte function in systemic lupus erythematosus

Interferon (IFN) production and responsiveness are abnormal in some patients with systemic lupus erythematosus (SLE). The present investigation was designed to further delineate these abnormalities of IFN response. The response to IFN-α was determined in peripheral blood mononuclear cells (PBMC) using the natural killer (NK) cell assay, the concanavalin A (Con A)-induced T-cell proliferation assay, and the pokeweed mitogen (PWM) blastogensis system. The average NK cell activity was impaired in SLE patients ( 19.7 ± 3.8 LU 10 7 cells ; n = 22 ) compared to 24 normal controls ( 45.6 ± 7.2 LU 10 7 cells ; n = 24 ) ( P < 0.05). In addition, the response to IFN in the NK cell system was impaired in SLE (110.0 ± 38.0% enhancement) compared to controls (320.0 ± 94.0% enhancement; ±SD P < 0.05). In contrast to the impaired IFN response of the NK cell in SLE, the effect of IFN on Con A- and PWM-induced blastogenesis in SLE was normal ( P > 0.1). Thus, the defect in IFN response in SLE appeared to be confined to the NK cell system, but was not present in the other assay systems. To determine if the impaired IFN response might be secondary to impaired release of natural killer cytotoxic factor (NKCF) induced by IFN, NKCF was generated from PBMC in the presence of IFN. IFN-induced NKCF release was markedly impaired in SLE (8.9 ± 11.7%) relative to normal controls (22.3 ± 11.2%) ( P < 0.05). IFN-induced release of NKCF in SLE also closely correlated with IFN-induced NK enhancement ( r = .83, P < 0.05). No depletion of NK cells was noted using the monoclonal antibody HNK-1. Thus, this study demonstrates for the first time that the insensitivity to IFN in SLE is not a universal lymphocyte defect but appears to be isolated to the NK cell which is functionally abnormal.

Suppression of Immunoglobulin Synthesis by Lymphocyte Subpopulations in Patients With Crohn's Disease

In previous studies, patients with mild or inactive Crohn's disease were found to have increased suppressor T-cell activity. To further characterize suppressor T cells in Crohn's disease, studies were carried out with the use of monoclonal antibodies. Excessive suppressor activity was eliminated by removal of OKT 8+ lymphocytes by complement-mediated lysis. However, the percentage of OKT 8+ (or Leu 2a+) cells and the ratio of OKT 4+ to OKT 8+ (or Leu 3a+ to Leu 2a+) cells were not significantly different from normal. Although the subgroup of patients with increased suppression of immunoglobulin synthesis had a significantly lower mean Leu 3a to Leu 2a ratio than that of normal subjects, in the whole group of Crohn's patients studied, neither the percentage of Leu 2a+ cells nor the ratio of Leu 3a+ to Leu 2a+ cells correlated with excessive suppression of immunoglobulin synthesis. A subpopulation of Leu 2a+ lymphocytes reactive with the monoclonal antibody HNK-1 (Leu 2a+ HNK-1+) was increased in patients with Crohn's disease. Furthermore, elimination of HNK-1-reactive lymphocytes by complement-mediated lysis diminished the excessive suppressor cell function in patients with Crohn's disease. The percentage of Leu 2a+ HNK-1+ lymphocytes correlated significantly with the suppression of pokeweed mitogen-stimulated immunoglobulin synthesis in vitro. Thus, patients with mild Crohn's disease have an increased suppressor cell activity in vitro which correlates with the presence of a subset of lymphocytes that have an HNK-1+ Leu-2a+ phenotype.

Characterization of human granular lymphocyte subpopulations expressing HNK-1 (Leu-7) and Leu-11 antigens in the blood and lymphoid tissues from fetuses, neonates and adults.

Three subpopulations of human granular lymphocytes from blood and lymphoid tissues were characterized using combinations of the monoclonal antibodies (mAb) HNK-1 (Leu-7), Leu-11 and VEP13. Each subpopulation was confirmed to possess natural killer (NK) cell functional capability, but a different level of cytotoxic efficiency (HNK-1+leu-11- less than HNK-1+Leu-11+ less than HNK-1-Leu-11+). In adult from 23 healthy donors, the subpopulations with HNK-1+Leu-11-, HNK-1+Leu-11+ and HNK-1-Leu-11+ phenotypes comprised 4.7 +/- 3.0, 8.0 +/- 6.4 and 3.9 +/- 3.5% of mononuclear cells, respectively. Despite their distinct surface marker phenotypes and NK functional ability, all 3 subpopulations exhibited granular lymphocyte morphology. One of these subpopulations, HNK-1+Leu-11-, also expressed the pan-T cell antigen Leu-4. Different patterns were observed in fetal bone marrow and cord blood, where the vast majority of HNK-1+ cells lacked the Leu-11 antigen (HNK-1+Leu-11+ cells). The HNK-1 antigen was not expressed on granulocytes and their precursors, whereas both Leu-11 and VEP13 antigens were expressed on these myeloid cells from fetal bone marrow and cord blood as well as adult bone marrow and spleen. Cell lines of granular lymphocytes cultured in the presence of interleukin 2 all possessed the HNK-1+Leu-4+ phenotype and NK functional capability but lacked the Leu-11 and VEP13 antigens on their surface after 15 days of culture. Although granular lymphocytes expressing the Fc receptors reacting with the mAb Leu-11 and VEP13, are the most functionally active NK cells, the HNK-1+ subpopulation lacking the Leu-11 and VEP13 antigens appears to be an important population (possibly an immature form of granular lymphocytes) for delineating the cell lineage(s) and differentiation of human granular lymphocytes. Although none of the currently available mAb react both inclusively and exclusively with human granular lymphocytes, the combination usage of these antibodies permits a more precise and comprehensive analysis of these subsets.

Recognition of myelin-associated glycoprotein by the monoclonal antibody HNK-1.

Myelin-associated glycoprotein (MAG) is a quantitatively minor component in both peripheral and central myelin sheaths that is thought to have a role in cell-cell interactions within the nervous system. We show here that a mouse monoclonal antibody, HNK-1, which is directed against human natural killer cells also recognizes an antigenic determinant of human central and peripheral nervous system white matter by immunoperoxidase staining of tissue sections. Immunoblot analysis of myelin proteins and purified extracted MAG indicates that the antigen recognized is MAG.

Involvement of the cytotoxic/suppressor T-cell subset in liver tissue injury of patients with acute and chronic liver diseases

So far, phenotypic and functional analyses of cytotoxic lymphocytes in viral hepatitis, as well as in primary biliary cirrhosis, have focused on circulating lymphocyte subpopulations, whereas their occurrence and distribution at the involved site, namely the liver, remain largely unknown. In the present study, monoclonal antibodies were used to characterize both circulating and liver-tissue-infiltrating lymphocyte subsets in acute cytomegalovirus hepatitis, in chronic B-virus hepatitis, and in primary biliary cirrhosis. Special emphasis was laid on the cytotoxic/suppressor T-cell subset. Total T cells were identified by the monoclonal antibody T411. The monoclonal antibody T811 was used to identify the cytotoxic/suppressor T-cell subset, which comprises virus-specific, altered self, and alloreactive cytolytic T lymphocytes and their precursors, a fraction of killer and natural killer cells. Furthermore, killer and natural killer cells were identified more specifically by the monoclonal antibody HNK1. Irrespective of the number of cytotoxic/ suppressor T cells in peripheral blood, these cells (T811 phenotype) were accumulated in the liver at the site of tissue injury. The preponderance of this lymphocyte subset at the site of tissue injury suggests an important role for these cells in the mechanism leading to tissue injury.

Natural killer cell activity in patients with multiple sclerosis given alpha interferon.

The purpose of this study was to examine the function and regulation of natural killer cells in vitro and in vivo in patients with multiple sclerosis. Of 12 patients who received 5 X 10(6) international units of human alpha interferon, 9 demonstrated an increase in natural killer cell activity within 48 hours as defined by the lysis of 51Cr-labeled K-562 cells. The activity was normal before treatment, unlike that of tumor-bearing patients, and reached baseline levels within one week despite continuous interferon administration over the next six months. The same patients given a placebo preparation failed to show this enhanced natural killer cell activity. We also studied K-562 killing in 36 other patients and age- and sex-matched control subjects and were unable to demonstrate any differences between the two groups or any correlation of natural killer cell function with disease activity. The in vitro augmentation of natural killer cell activity by purified measles virions, which is associated with the release of interferon, and by the isolated glycoproteins of measles virus, which activates natural killer cells without the extracellular release of interferon, was similar in both patients and control subjects. Further, the proportion of cells defined by the monoclonal antibody HNK-1, which defines both natural killer cells and a small subset of cytotoxic T lymphocytes, was normal. In patients with multiple sclerosis, the normality of natural killer cell function, as defined by these several interrelated assays, speaks against a defect in this nonspecific antiviral defense mechanism in the pathogenesis of the disease.

Severe combined immunodeficiencies, primary T-cell defects and DiGeorge syndrome in humans: Characterization by monoclonal antibodies and natural killer cell activity

Peripheral blood mononuclear cells from three patients with severe combined immunodeficiency (SCID), three with SCID whether B cell positive or with pure T-cell defect, and two with DiGeorge syndrome were analyzed with a panel of monoclonal antibodies against immature and mature T-cell subsets. Natural killer (NK) cells were enumerated by the use of the HNK-1 monoclonal antibody. NK activity against the K562 and MOLT 4 cell lines was also investigated. According to the monoclonal antibodies profile and the NK activity, patients could be divided into three groups. Patients with classical SCID had no detectable circulating T cells as well as NK cells and activity, probably due to an early block in stem cell differentiation. Patients affected by SCID with B cells or pure T cell defect showed a decrease in lymphocytes with mature phenotypes but prothymocytes or immature thymocytes circulated in peripheral blood. Children with DiGeorge syndrome had a decrease in mature thymocytes and, in this study, NK cells were normal. These data help to clarify both the preeminent immunologic features of SCID and related syndromes and the character of NK cells.

Depressed levels of granular lymphocytes with natural killer (NK) cell function in 247 cancer patients.

The HNK-1 (Leu-7) monoclonal antibody was used to enumerate and characterize the level of blood granular lymphocytes in 247 cancer patients. The results were compared to 146 control individuals. A fluorescence-activated cell sorter was used to purify blood HNK-1+ cells from cancer patients. The monoclonal antibody identified a homogeneous population of granular lymphocytes with greater than 95% purity. Conversely, virtually 100% of HNK-1- cells from cancer patients were agranular lymphocytes. These results were the same as previously observed in normal individuals, where the HNK-1+ cell fraction contained all the lymphocytes with spontaneous cytotoxicity in natural killer (NK) and killer (K) cell assays. The level of HNK-1+ cells in cancer patients correlated significantly with the patient's age and sex, with older individuals having higher levels and male patients containing a higher proportion than female patients. The levels in the cancer patients were significantly lower than normal controls (p = 0.04). When the results were subdivided by the histologic type of cancer, additional differences were noted. Compared to age and sex-matched controls, significantly depressed levels of HNK-1+ granular lymphocytes were observed in 49 patients with colon cancer (9.7% vs. 15.8%, p = 0.0001), 18 patients with lung carcinoma (11.7% vs. 27.0%, p = 0.0001), 24 patients with breast carcinoma (12.0% vs. 15.5%, p = 0.04) and 64 patients with head and neck carcinoma (15.9% vs. 19.1%, p = 0.05). However, there were no significant differences overall in the average HNK-1+ cell level of 66 patients with melanoma (13.0% vs. 13.5%, p = 0.75) and nine patients with sarcomas (15.8% vs. 14.3%, p = 0.71). Thus, this important subpopulation of granular lymphocytes with NK and K cell function was significantly depressed in most cancer patients. Accounting for the patient's age and sex and the histologic type of cancer was critical to interpreting the results.

Enhancing antibodies and suppressor cells in pregnancy: Role of the placentation

This chapter reviews the characterization of human natural killer (NK) cells identified by the monoclonal HNK-1 (Leu-7) antibody. The monoclonal antibody, HNK-1, was produced against the cultured cell line, HSB-2, using the hybridoma technique introduced by Köhler and Milstein. Although HSB-2 cells have been considered to be of T-cell origin, they lack T-cell-associated antigens identified by the monoclonal antibodies, OKT1, T3, T4, T5, and T8. In a study described in the chapter, when the HNK-1 antibody was tested against cultured lymphoid cell lines, it reacted with some T-cell lines (HSB-2 and MOLT-4) but not with any other T-cell line (MOLT-3), with any B-cell lines, or with cultured phagocytic cells. When human blood mononuclear cells were examined by immunofluorescence, the HNK-1 antibody reacted solely with a morphologically distinct population of granular lymphocytes with NK- and K-cell function. The results suggested that a differentiation antigen identified by the monoclonal HNK-1 antibody is exclusively expressed on human NK and K cells. The HNK-1 antibody also distinguishes the classically defined NK cell from its analogues.

Expression of C3b receptors on human be cells and myelomonocytic cells but not natural killer cells.

We have examined natural killer (NK) cells, B cells and myelomonocytic cells at different stages of differentiation for the expression of surface C3b receptors (C3bR). Receptor presence was detected using affinity-purified F(ab')2 anti-C3bR antibodies in indirect immunofluorescence assays. NK cells, identified in fetal and adult tissues by the monoclonal antibody HNK-1, were C3bR- except for infrequent C3bR+ HNK-1+ cells in some blood samples. NK cells were not induced to express C3bR by exposure to interferon, target cells, or phorbol myristate acetate. B cells gradually acquired the ability to express C3bR with maturity: 15% of large pre-B cells were C3bR+, 35 to 48% of small pre-B, 60 to 80% of immature B, and 99% of mature B cells. Mature plasma cells were rarely C3bR+. Myelomonocytic cells acquire C3bR relatively late during their development, with neutrophils beginning to express C3bR during the band stage of differentiation. All adult blood myelomonocytic lineage cells, identified by the monoclonal antibody MMA and by morphology, were C3bR+.

Suppressor cell function of human granular lymphocytes identified by the HNK-1 (Leu 7) monoclonal antibody.

The HNK-1 (Leu 7) differentiation antigen defines a subpopulation of human granular lymphocytes with natural killer (NK) and K cell function. In this study, we investigated whether HNK-1+ cells, identified with the monoclonal antibody and purified with a fluorescence-activated cell sorter (FACS), could function as suppressor cells. The results demonstrated that purified HNK-1+ cells efficiently suppressed both PWM-induced IgG production by B cells and T cell proliferation in mixed lymphocyte reactions (MLR). Manifestation of this suppressor cell activity required immune complex activation and was partially sensitive to 2000 rad irradiation. This suppressor cell activity was predominantly mediated by a subset of HNK-1+ cells that have previously been shown to have maximum NK function and lack expression of the E rosette (ER) receptor and T cell antigens (e.g., T3 and T8). Thus, HNK-1+ER- cells suppressed a MLR by an average 52%; HNK-1+ER+ were one-half as efficient, causing an average 23% suppression. For comparison, we also examined the characteristics of Leu 2a+ suppressor T lymphocytes. In contrast to HNK-1+ cells, unactivated Leu 2a+ cells suppressed both B and T cell responses. This suppressor activity was not augmented by immune complex activation and was absolutely radio-sensitive in PWM assays. HNK-1+ cells, especially the HNK+ER- subset, can therefore mediate suppressor cell function in addition to their spontaneous cytotoxic function. Furthermore, some of their suppressor cell properties are distinct from those attributed to other types of suppressor lymphocytes.

Characterization of HNK-1 + (Leu-7) human lymphocytes : III. Interferon effects on spontaneous cytotoxicity and phenotypic expression of lymphocyte subpopulations delineated by the monoclonal HNK-1 antibody

Interferon (IFN) augments the cytotoxic function of natural killer (NK) and killer (K) cells. We have previously shown that all NK- and K-cell function resides in the HNK-1 + population of granular lymphocytes. The present experiments demonstrated that IFN significantly augmented the efficiency of purified HNK-1 + cells to perform both NK- and K-cell function. In contrast, HNK-1 − cells could not lyse target cells even in the presence of IFN. IFN did not generate new HNK-1 + cells from the pool of HNK-1 − cells. We then examined the possibility that IFN might induce the maturation of immature NK cells previously defined as having an HNK +T3 + phenotype and a paucity of cytoplasmic granules. However, no changes were observed either in the proportion of HNK-1 + cells expressing the T3 antigen or in the number of granules within each HNK-1 + cell even after an 18-hr incubation with IFN. While fresh HNK-1 − cells lack NK-cell function, they can acquire NK-like activity without expressing the HNK-1 antigen after incubation with either alloantigens or mitogens. When incubated further with IFN, these alloantigen- or PHA-activated HNK-1 − cells with NK-like activity demonstrated relatively little augmentation of their cytotoxicity. It is concluded that interferon exerts its influence on restricted subpopulations of cells, primarily HNK-1 + cells. Its mechanism appears to concern the cytotoxic event rather than influencing cellular maturation.

Characterization of HNK-1+ (Leu-7) human lymphocytes. I. Two distinct phenotypes of human NK cells with different cytotoxic capability.

Human lymphocytes with NK and K cell activities can be identified by the HNK-1 (Leu-7) monoclonal antibody. In these experiments, subsets of HNK-1+ cells from blood and bone marrow were distinguished by their expression of other cell surface antigens, their morphology, and their NK functional capability. Two-color immunofluorescence analysis revealed that subpopulations of HNK-1+ cells in blood expressed antigens found on mature T cells (e.g., T1, T3, T4, T8), but none expressed antigens characteristic of immature T cells (T6, T9). The majority of HNK-1+ cells (greater than 60%) also expressed a myeloid antigen (M1), whereas a minority (less than 25%) expressed HLA-DR. HNK-1+ cells were separated into T3- and T3+ subsets with the fluorescence-activated cell sorter and analyzed for their morphology and NK cell function. HNK+T3- cells exhibited a high level of NK activity against K562 target cells and contained many cytoplasmic granules. On the other hand, HNK+T3+ cells had low NK activity and a paucity of cytoplasmic granules. The cell sizes of HNK+T3- and HNK+T3+ cells were indistinguishable by light-scatter analysis. When these cell fractions were analyzed further, a reciprocal relationship between T3 and M1 antigen expression was observed. These results thus delineate two distinct subsets of human HNK-1+ cells in blood with different cytotoxic capability: HNK+T3-M1+ and HNK+T3+M1- cells. Analysis of bone marrow cells demonstrated that only 0.7% of the nucleated cells expressed the HNK-1 antigen; virtually all of these cells expressed both the T3 and T8 antigens but lacked the M1 antigen. Thus, a majority of HNK-1+ cell population in blood were T3-M1+, whereas almost all bone marrow HNK-1+ cells were T3+M1-. We propose that these subsets of cells represent different stages in NK cells differentiation.

Natural killer (HNK-1+) cells in Chediak-Higashi patients are present in normal numbers but are abnormal in function and morphology.

Children with the Chediak-Higashi (CH) syndrome are known to have abnormalities of natural killer (NK) cell function. We used the HNK-1 monoclonal antibody that reacts specifically with human NK and K cells to distinguish whether this abnormality was due either to a numerical deficiency of NK cells or a defect in their ability to function. In eight CH patients, a significant proportion of their blood mononuclear cells (10--19%) expressed the HNK-1 differentiation antigen. The level of NK cells in the five children with CH syndrome was higher than for age-matched normal controls (15.8% vs. 5.8%, P less than 0.001). When HNK-1+ cells were isolated with a fluorescence-activated cell sorter, the NK cells from CH patients were a homogeneous population of lymphocytes with a single large granule rather than the multiple small granules seen in Nk cells from normal individuals. The purified HNK-1+ cells from the CH patients had minimal NK or K cell function. The CH syndrome thus includes a functionally defective population of NK cells that retain the capability of expressing the HNK-1 differentiation antigen.