Pathogenesis of the natural killer cell deficiency in AIDS

Editorial to the Special Issue "Clinical Immunology in Italy, with Special Emphasis to Primary and Acquired Immunodeficiencies: A Commemorative Issue in Honor of Prof. Fernando Aiuti"

Fernando Aiuti (Figure 1), born in Urbino on 8 June 1935, suddenly died on 9 January 2019, leaving a great void not only among his family members and those who knew him and appreciated his great humanity and acute intelligence, but in the entire immunological scientific community [...].

Monkeying Around: Using Non-human Primate Models to Study NK Cell Biology in HIV Infections

Natural killer (NK) cells are the major innate effectors primed to eliminate virus-infected and tumor or neoplastic cells. Recent studies also suggest nuances in phenotypic and functional characteristics among NK cell subsets may further permit execution of regulatory and adaptive roles. Animal models, particularly non-human primate (NHP) models, are critical for characterizing NK cell biology in disease and under homeostatic conditions. In HIV infection, NK cells mediate multiple antiviral functions via upregulation of activating receptors, inflammatory cytokine secretion, and antibody dependent cell cytotoxicity through antibody Fc-FcR interaction and others. However, HIV infection can also reciprocally modulate NK cells directly or indirectly, leading to impaired/ineffective NK cell responses. In this review, we will describe multiple aspects of NK cell biology in HIV/SIV infections and their association with viral control and disease progression, and how NHP models were critical in detailing each finding. Further, we will discuss the effect of NK cell depletion in SIV-infected NHP and the characteristics of newly described memory NK cells in NHP models and different mouse strains. Overall, we propose that the role of NK cells in controlling viral infections remains incompletely understood and that NHP models are indispensable in order to efficiently address these deficits.

Effects of simulated microgravity on primary human NK cells

The deleterious effects of microgravity on lymphocytes have been demonstrated in previous studies. However, research on the effects of microgravity on human natural killer (NK) cells remains exceedingly limited. In this study, we demonstrated that NK cell cytotoxicity was significantly decreased under simulated microgravity (SMG) conditions (p<0.05). Several processes, including apoptosis, receptor expression, and cytokine secretion, were investigated in human NK cells under SMG. We observed decreased cytotoxicity, concurrent with increased apoptosis and necrosis, in NK cells after exposure to SMG (p<0.05). Additionally, interferon (IFN)-γ and perforin expression decreased significantly, and the expression of granzyme-B was only slightly reduced. Meanwhile, SMG selectively inhibited the expression of certain surface receptors on NK cells. Specifically, the expression of NKG2A and NKG2D were significantly downregulated under SMG, but the expression of NKp30 and NKp44 was not affected. We also found that interleukin (IL)-15 alone or in combination with IL-12 could counteract the inhibition of NK cell cytotoxicity under SMG. Our findings indicate that human NK cells were sensitive to SMG, as reflected by their decreased cytotoxicity. Factors such as increased early apoptosis and late apoptosis/necrosis and the decreased expression of INF-γ, cytolytic proteins, and cell surface receptors may be responsible for the loss of cytotoxicity in human NK cells under SMG. A combination of IL-12 and IL-15 may be useful as a therapeutic strategy for overcoming the effects of microgravity on human NK cells during long space missions.

Recombinant interleukin-2 (rIL-2) in acquired immune deficiency syndrome (AIDS): Preliminary report in patients with lymphoma associated with HIV infection

In an ongoing phase II study, 12 patients with lymphoma and HIV infection were treated with zidovudine (ZDV) and recombinant interleukin-2 (rIL-2) to evaluate if this association may produce beneficial effect on the immunologic status and the outcome of lymphoma. The protocol included daily doses of rIL-2 at 6 MIU/m2 over 5 days in c.i. per week for a total 4 courses; ZDV was associated at 600 mg/d in the period under study. An improved CD4 count, exceeding 2- to 4-fold the basal count, was obtained in patients with a basal CD4 number greater than 100/microliters accompanied by a significant increase of NK and LAK activity (p less than 0.001). From the clinical point of view the reduction of tumor manifestation was proportional to CD4 basal number; 2 patients from those with CD4 greater than 100/microliters obtained a complete remission after rIL-2 and ZVD. The p24 antigen, taken as parameter of viral replication, remained invariably negative after rIL-2 and ZDV in patients already negative and became negative in 1 patient previously positive. Our conclusion is that the association of rIL-2 and AZT is safe and useful in patients with lymphoma and HIV infection.

Augumentation of natural killer activity with exogenous interleukins in patients with HIV and pulmonary tuberculosis coinfection

A depressed level of natural killer (NK) activity is one of the various immunological abnormalities in HIV infection. Defective NK cell functions can be partially restored in vitro by interleukin (IL)-2 and IL-12. IL-15 shares receptor and several biological properties with IL-2. The effect of IL-15 on NK cells in patients with HIV and tuberculosis coinfection (HIV-TB) is unclear. This study examined the cytotoxic activity and cytokine response of NK cells in HIV-TB after stimulation with IL-15 and IL-12/IL-2. The study includes 16 normal healthy subjects (NHS), 15 patients with pulmonary tuberculosis (TB), 15 HIV-infected subjects (HIV), and 15 HIV-TB patients. The cytotoxic activity of NK cells was assessed by dioctadecyloxacarbocyanine dye-based flow cytometry. Interferon-gamma present in the culture supernatants was measured by enzyme-linked immunosorbent assay. Basal NK cytotoxicity was found to be lower in HIV-TB (p < 0.05) and HIV when compared to NHS or TB. Maximal NK cytotoxicity (p < 0.05) was observed with an IL-15 and IL-12 combination in all the groups. At a 50:1 effector/target ratio, the mean fold increase in NK cytotoxicity upon stimulation was 2.11 for HIV and 1.84 for HIV-TB. Interferon-gamma levels from the stimulated cultures were elevated (p < 0.05) in the HIV and HIV-TB groups. We found no correlation between NK cytotoxicity and CD4 counts in HIV-TB. There is a positive correlation between NK cytotoxicity and interferon-gamma secretion for HIV-TB. The combination of IL-15 and IL-12 may have potential to improve the NK activity of HIV and HIV-TB.

Dendritic cells from HIV-1 infected individuals are less responsive to toll-like receptor (TLR) ligands

We compared TLR responsiveness in PBMC from HIV-1-infected and uninfected individuals using the TLR agonists: TLR7 (3M-001), TLR8 (3M-002), and TLR7/8 (3M-011). Activation and maturation of plasmacytoid dendritic cells (pDC) were measured by evaluating CD86, CD40, and CD83 expression and myeloid dendritic cell (mDC) activation was measured by evaluating CD40 expression. All agonists tested induced activation and maturation of pDC in PBMC cultures of cells from HIV+ and HIV- individuals. The TLR7 agonist induced significantly less pDC maturation in cells from HIV+ individuals. Quantitative assessment of secreted IFN-alpha and pro-inflammatory cytokines at the single cell level showed that pDC from HIV+ individuals stimulated with TLR7 and TLR7/8 induced IFN-alpha. TLR8 and TLR7/8 agonists induced IL-12 and COX-2 expression in mDC from HIV+ and HIV- individuals. Understanding pDC and mDC activation and maturation in HIV-1 infection could lead to more rational development of immunotherapeutic strategies to stimulate the adaptive immune response to HIV-1.

Switch from inhibitory to activating NKG2 receptor expression in HIV-1 infection: lack of reversion with highly active antiretroviral therapy

BACKGROUND

HIV-1 infection is characterized by increase in inhibitory receptors and loss of activating receptors on natural killer (NK) cells, resulting in loss of cell activity. Exceptionally, for an inhibitory receptor, the proportion of NK cells bearing CD94-NKG2A decreases during HIV-1 infection. It is not understood whether HIV-1 itself or other concomitant infections drive these changes.

OBJECTIVES

To investigate the relationship between HIV-1 viraemia and changes in C-type lectin-like receptor expression in NK cells and to investigate the effect of highly active antiretroviral therapy (HAART) on these changes.

METHODS

Three cohorts of patients were studied: (1) before, during and after treatment interruption in aviraemic and viraemic patients receiving HAART (n = 15); (2) HIV-1-positive treatment-naive individuals (n = 13); and (3) HIV-1-positive individuals receiving successful HAART for a minimum of 1 year without interruption (n = 11). Flow cytometry was used to study the expression of NKG2A before and after treatment interruption and to define expanded populations of NK cells in untreated and treated HIV-1-positive individuals. Assays were performed in vitro to assess the cytotoxicity of the expanded populations.

RESULTS

Increases in plasma HIV-1 RNA during treatment interruption in aviraemic HAART-treated individuals did not influence the proportion of NK cells carrying the complex CD94-NKG2A. Loss of NKG2A NK cells corresponded to the dramatic expansion of a distinct population of cells expressing a functional activating CD94-NKG2C receptor with skewed expression of killer cell immunoglobulin-like receptor family and natural cytotoxicity receptors.

CONCLUSION

Changes in the NK cell repertoire during HIV-1 infection were not a result of HIV-1 viraemia alone but resembled those associated with concomitant infections.

Increased natural killer cell activity in viremic HIV-1 infection

NK cells are a subset of granular lymphocytes that are critical in the innate immune response to infection. These cells are capable of killing infected cells and secreting integral cytokines and chemokines. The role that this subset of cytolytic cells plays in HIV infection is not well understood. In this study, we dissected the function of NK cells in viremic and aviremic HIV-1-infected subjects, as well as HIV-1-negative control individuals. Despite reduced NK cell numbers in subjects with ongoing viral replication, these cells were significantly more active in secreting both IFN-gamma and TNF-alpha than NK cells from aviremic subjects or HIV-1-negative controls. In addition, NK cells in subjects with detectable viral loads expressed significantly higher levels of CD107a, a marker of lysosomal granule exocytosis. The expression of CD107a correlated with NK cell-mediated cytokine secretion and cytolytic activity as well as with the level of viral replication, suggesting that CD107a represents a good marker for the functional activity of NK cells. Finally, killer Ig-related receptor+ NK cells were stable or elevated in viremic subjects, while the numbers of CD3-/CD56+/CD94+ and CD3-/CD56+/CD161+ NK cells were reduced. Taken together, these data demonstrate that viremic HIV-1 infection is associated with a reduction in NK cell numbers and a perturbation of NK cell subsets, but increased overall NK cell activity.

Loss of the CD56hiCD16- NK cell subset and NK cell interferon-gamma production during antiretroviral therapy for HIV-1: partial recovery by human growth hormone

Previous studies have shown that human natural killer (NK) cells are lost from the periphery and are functionally suppressed during HIV-1 infection, and that the administration of highly active antiretroviral therapy (HAART) results in a recovery of NK cell numbers in HIV-1-infected individuals. However, despite this recovery, interleukin (IL)-2 + IL-12-driven interferon (IFN)-gamma production by NK cells has been shown to remain suppressed after HAART. Here we show that the innate immune factor IL-15 in combination with IL-12 is also unable to recover NK cell IFN-gamma production in HAART-treated individuals. Furthermore, we also demonstrate an imbalance in the distribution of CD56loCD16hi and CD56hiCD16- NK subsets after successful HAART, CD56hiCD16- cells being reduced substantially in HIV-1 patients on HAART. Treatment of patients with combined human growth hormone and antiretroviral therapy resulted in further enhancement in the absolute numbers and the proportion of NK cells in some individuals in the absence of parallel effects on CD4+ T cells. Furthermore, in these individuals HAART with growth hormone resulted in an enhancement of cytokine-driven NK cell activation and IFN-gamma production compared to the HAART-only baseline.

Effects of stress management on PNI-based outcomes in persons with HIV disease

A pretest-posttest, repeated-measures design was used to evaluate the effects of two stress management interventions on a battery of outcomes derived from a psychoneuroimmunological (PNI) framework. The effects of cognitive-behavioral relaxation training groups (CBSM) and social support groups (SSG) were compared with a WAIT-listed control group on the outcomes of psychosocial functioning, quality of life, neuroendocrine mediation, and somatic health. Participants were 148 individuals (119 men, 29 women), diagnosed with HIV disease; 112 (76%) completing the study groups. Using analysis of covariance, the CBSM group was found to have significantly higher postintervention emotional well-being and total quality-of-life scores than did either the SSG or WAIT groups. SSG participants had significantly lower social/family well-being scores immediately postintervention and lower social support scores after 6 months. The findings point to a pressing need for further, well-controlled research with these common intervention modalities.

Enhancement of natural killer cell activation and antibody-dependent cellular cytotoxicity by interferon-alpha and interleukin-12 in vaginal mucosae Sivmac251-infected Macaca fascicularis

We studied the innate immune system of Cynomolgus monkeys (Macaca fascicularis) experimentally infected via the vaginal mucosae with a virulent simian immunodeficiency virus isolate SIVmac251. Animals were evaluated for their natural killer (NK) cell activity, and for their antibody-dependent cellular cytotoxicity. NK cells from SIVmac251-infected macaques show impaired NK cell activity compared to cells from uninfected animals. Subsequent treatment of NK cells with interferon-a (IFN-alpha) or interleukin-12 (IL-12) alone partially restored the NK activity. However, either treatment of NK cells with both IFN-alpha and IL-12 completely reversed the impairment of cytotoxicity induced by simian immunodeficiency virus (SIV) infection. Incubation of NK cells from infected but not from uninfected monkeys with IFN-alpha and IL-12 for 8 days increased the percentage of CD16+/CD56+ cells twofold to five-fold and enhanced antibody-dependent cellular cytotoxicity (ADCC) activity. Thus IFN-alpha and IL-12 greatly enhance both the NK cell and ADCC activities of peripheral blood cells from SIVmac251-infected animals and increase the number of NK cells in longer term culture. The combined effect of IFN-alpha and IL-12 in enhancing NK cell activity may provide a novel therapeutic approach for the restoration of depressed NK cell activity observed in human immunodeficiency virus (HIV)-infected patients.

Immune reconstitution

Immune reconstitution in HIV-infected patients remains a potential mechanism to explain delayed disease progression and increased survival following suppressive therapy. Many discrepancies remain to be studied. Is an immune response to HIV protective? Why are anti-HIV CD4 responses lost so quickly in progressors and how can they be restored? What is the damage to the immune system that occurs early in disease and why can it not be overcome by simply controlling viral replication? Will management of immune reconstitution be used in future adjunct treatment strategies (vaccine or STI)? Because HAART is not the answer to long-term management of HIV throughout the world, the recovery of immune function and it's potential to control viral replication remains a key goal in the long-term management of HIV-infected persons.

Sustained impairment of IFN-gamma secretion in suppressed HIV-infected patients despite mature NK cell recovery: evidence for a defective reconstitution of innate immunity

The impairment of NK cell functions in the course of HIV infection contributes to a decreased resistance against HIV and other pathogens. We analyzed the proportion of mature and immature NK cell subsets, and measured subsets of IFN-gamma and TNF-alpha-producing NK and T cells in viremic or therapy-suppressed HIV-infected subjects, and noninfected control donors. Viremic HIV(+) individuals had significantly lower proportions of mature CD3(-)/CD161(+)/CD56(+) NK cells and of IFN-gamma-producing NK cells compared with noninfected donors, independent of CD4(+) T cell counts. HIV-infected subjects with undetectable viral load recovered mature CD3(-)/CD161(+)/CD56(+) NK cells and cytotoxicity against tumor (K562) and HSV-infected target cells to percentages comparable with those of uninfected individuals, but their NK cells remained impaired in their ability to produce IFN-gamma. In parallel to these ex vivo findings, in vitro NK cell differentiation of CD34-positive cord blood precursors in the presence of R5 or X4 HIV-1 resulted in the production of NK cells with a normal mature phenotype, but lacking the ability to produce IFN-gamma, whereas coculture of uninfected PBMC with HIV failed to affect mature NK cell properties or IFN-gamma secretion. Altogether, our findings support the hypothesis that mature NK cell phenotype may be uncoupled from some mature functions following highly active antiretroviral therapy-mediated suppression of HIV-1, and indicate that relevant innate immune functions of NK cell subsets may remain altered despite effective viral suppression following antiretroviral treatment.

Development of a novel allo-independent HIV-1 virus preparation for use in immunoassays

The study of the immunologic response to whole human immunodeficiency virus type 1 (HIV-1) antigen is limited by the presence of highly immunogenic human leukocyte antigen (HLA) alloantigens on the envelope of wild type virus. This paper outlines the production of HIV-1 infectious virions free of HLA for use as whole viral antigens in immunoassays. An infectious molecular clone of HIV-1 was transfected into the K-562 cell line, which does not express HLA on the cell surface. After a 30-day selection period, to ensure stable transfection, cells and culture supernatants were analyzed for productive HIV-1 infection and virion infectivity. An enzyme-linked immunosorbent assay (ELISA) confirmed the presence of p24 in the culture supernatants. Molecular confirmation of HIV-1 transfection was achieved by gene amplification. Flow cytometric analysis was used to identify gp120 on the surface of the infected cells. Viral supernatants were tested for HIV infectivity in peripheral blood mononuclear cells (PBMCs). The usefulness of this viral preparation as whole virus antigens was validated using PBMCs from HIV-infected individuals. These results indicate the successful production of HIV-1 infectious virions, which do not have HLA molecules on their viral envelope, and demonstrate their utility for immunoassays.

Persistent HIV-1 infection of natural killer cells in patients receiving highly active antiretroviral therapy

We have identified a subset of CD56(+)CD3(-) human natural killer (NK) cells that express CD4 and the HIV coreceptors CCR5 and CXCR4. These cells can be productively infected in vitro by both CCR5- and CXCR4-using molecular clones of HIV-1 in a CD4-dependent manner. Analysis of HIV-infected persons showed that viral DNA is present in purified NK cells, and virus could be rescued from these cells after in vitro cultivation. Longitudinal analysis of the HIV-1 DNA levels in NK cells from patients after 1-2 years of highly active antiretroviral therapy indicated that NK cells remain persistently infected and account for a substantial amount of the viral DNA in peripheral blood mononuclear cells. These results demonstrate that a subset of non-T cells with NK markers are persistently infected and suggest that HIV infection of NK cells is important for virus persistence. The properties of the virus reservoir in these cells should be considered in attempts to further optimize antiretroviral therapies.

NK cell activation by dendritic cells is dependent on LFA-1-mediated induction of calcium-calmodulin kinase II: inhibition by HIV-1 Tat C-terminal domain

In this study, we show that binding to autologous dendritic cells (DC) induces a calcium influx in NK cells, followed by activation of the calcium-calmodulin kinase II (CAMKII), release of perforin and granzymes, and IFN-gamma secretion. CAMKII is induced via LFA-1: indeed, oligomerization of LFA-1 leads to CAMKII induction in NK cells. Moreover, release of lytic enzymes and cytotoxic activity is strongly reduced by masking LFA-1 or by adding CAMKII inhibitors such as KN62 and KN93, at variance with the inactive compound KN92. NK cell-mediated lysis of DC and IFN-gamma release by NK cells upon NK/DC contact are inhibited by exogenous HIV-1 Tat: the protein blocks calcium influx and impairs CAMKII activation elicited via LFA-1 in NK cells, eventually inhibiting degranulation. Experiments performed with synthetic, overlapping Tat-derived peptides showed that the C-terminal domain of the protein is responsible for inhibition. Finally, both KN62 and Tat reduced the extension of NK/DC contacts, possibly affecting NK cell granule polarization toward the target. These data provide evidence that exogenous Tat inhibits NK cell activation occurring upon contact with DC: this mechanism might contribute to the impairment of natural immunity in HIV-1 infection.

Relative preservation of natural killer cell cytotoxicity and number in healthy AIDS patients with low CD4 cell counts

OBJECTIVE

This study examines whether there may be an immune component that protects a relatively rare group of HIV-infected people with very low CD4 cell counts (< or = 50 x 10(6)/l) who have prolonged asymptomatic periods.

DESIGN/METHODS

Three groups were recruited in Miami: (i) healthy low CD4 cell count patients (HLC; n = 30) who, for 9 months had < 50 x 10(6) CD4 cells/l, were asymptomatic and were not on protease inhibitors during that time; (ii) HIV comparison group (Comp; n = 60) who had CD4 cell counts predominantly 150 x 10(6) to 400 x 10(6)/l and never had AIDS Category C symptoms; this group was also followed for CD4 cell count and viral load change over 6 months; and (iii) healthy community controls (n = 33). The study was replicated at the University of California at Los Angeles (UCLA) with HLC (n = 31) versus HIV-negative laboratory controls (n = 28).

RESULTS

The HLC patients were significantly higher than the Comp group on natural killer cell cytotoxicity (NKCC) and natural killer cell number (NK#) despite their lower CD4 cell numbers and higher viral loads. In fact, there was no difference between the HLC group and the healthy community control group in NK# or NKCC. The NK findings were replicated at UCLA. A retrospective analysis showing that higher NKCC was related to fewer prior symptoms in the HLC group, and prospective analysis in the Comp group showing that NK# predicted a lower increase in viral load over 6 months further supported the importance of NK# and NKCC.

CONCLUSIONS

Non-specific cellular immunity may be a factor protecting the health of HIV sero-positive individuals with very low CD4 cell counts.

Changes in Lymphocyte Subsets in Depressed HIV-Infected Patients Without Antiretroviral Therapy

The authors studied the effects of major depression on lymphocyte subsets by comparing depressed and matched control subjects in a population of HIV-seropositive outpatients not treated with antiretroviral therapy. Twelve patients with major depression, as determined by the Structured Clinical Interview for DSM-III-R, were assessed in comparison with 15 matched nondepressed control subjects. Flow cytometric analysis of peripheral blood lymphocyte subsets together with immunological parameters were performed. In HIV-infected patients, major depression was significantly (P=0.001) associated with a reduction in natural killer cell absolute count and percentage. This report suggests that depression may alter the natural killer cell population that provides a cytotoxic defense against HIV infection.

Inhibition of natural killer cell cytotoxicity and interferon gamma production by the envelope protein of HIV and prevention by vasoactive intestinal peptide

Natural killer (NK) cell dysfunction is common in human immunodeficiency virus (HIV)-infected subjects, although its mechanisms are poorly understood. A direct effect of HIV envelope glycoprotein gp120 may be involved. We investigated the in vitro effects of gp120 on the major NK cell effector functions, natural cytotoxicity and cytokine production. In addition, the ability of the vasoactive intestinal peptide (VIP) to modulate these effects was investigated. Our results indicated that gp120 inhibits NK natural cytotoxicity and showed, for the first time, that the inhibition affects also the production of the proinflammatory cytokine interferon-gamma (IFN-gamma). Interestingly, the inhibitory effect on NK cell functions was obtained with gp120 at concentrations within the range measured in the serum of HIV-infected subjects. Furthermore, we showed that the inhibitory activity of gp120 can be prevented by coincubation with VIP, even if VIP has no stimulatory activity by itself. Taken together these data suggest that (1) an inhibitory effect of gp120 may account for the NK cell dysfunction in HIV-infected subjects; (2) the gp120-mediated decrease in IFN-gamma production by NK cells may contribute to the cytokine imbalance observed in HIV infection; and (3) VIP counteracts the inhibitory effect of gp120 on NK cell functions.

High versus low basal cortisol secretion in asymptomatic, medication-free HIV-infected men: differential effects of severe life stress on parameters of immune status

The authors hypothesized that HIV-infected men with high basal cortisol secretion would exhibit greater stress-related reductions in the ratio of Th1/Th2 cell-derived cytokines and numbers of CD8+ T and NK lymphocytes than low basal cortisol secretors. A semistructured interview was used to assess life stress during the preceding 6 months of 94 HIV-infected men classified as high and low cortisol secretors (n = 47/group). Increased levels of severe life stress were highly correlated with lower numbers of CD8+ T cells, CD16+ and CD56+ NK cells, CD57+ cells, and higher DHEA-S concentrations in the high cortisol group. Conversely, no significant correlations were found in the low cortisol group. No correlations were found between stress and CD4+ T helper/inducer cell counts, cytokine production, or testosterone levels in either participating group. These data suggest that severe stress in combination with high glucocorticoid activity may modify select parameters of immune status in HIV-infected men.

Role of T cell subsets in the modulation of Mycobacterium avium growth within human monocytes

Mycobacterium avium frequently causes disseminated disease in patients with advanced AIDS with low CD4 counts. The effects of T lymphocyte on intracellular M. avium replication were examined. Plastic adherent monocytes and nonadherent lymphocytes were separated from peripheral blood mononuclear cells. After infection with M. avium, monocytes were cultured with or without autologous lymphocytes (1-10 cells/monocyte) for up to 7 days. Addition of lymphocytes to M. avium-infected monocytes significantly decreased intracellular M. avium growth after 7 days culture (n = 11, P < 0.01, paired t test) and increased IFN-gamma production compared to monocytes alone. Neutralizing IFN-gamma partially abrogated lymphocyte activity. CD4 depletion diminished anti-mycobactericidal effects and CD8(+) lymphocytes increased intracellular M. avium growth (P < 0.05, n = 5, t test). These data suggest that interactions between monocytes and nonadherent cell fractions such as CD4(+) T cells and NK cells are important in intracellular M. avium growth modulation in monocytes from healthy humans.

Differential production of IFN-gamma, analyzed at the single-cell level, by specific subsets of human NK and T cells from healthy and HIV(+) subjects

BACKGROUND

Interferon gamma is a cytokine that plays a central role in immunity, and is physiologically secreted by T and NK cells under appropriate stimuli during the immune response. By means of flow cytometry, we performed a single cell analysis of interferon gamma producing NK cells and their surface phenotype in normal and HIV(+) individuals that show several defects of cytokine production and cellular immunity.

METHODS

PBMC or purified NK cells were stimulated for 1-12 h with PMA/ionomycin in the presence of monensin, subsequently stained for surface CD56 and CD3 or CD8, and for intracytoplasmic IFN-gamma, and analysed by flow cytometry.

RESULTS

Our results show that CD56(+) NK cells are more efficient interferon gamma producers than T cells. Moreover, within the CD56(+) NK cell population, those that co-express low density CD8 are the best producers. Finally, we show that NK cells during HIV infection are more massively recruited to interferon gamma production than those from normal subjects.

CONCLUSIONS

Both in the normal and HIV(+) subjects, a higher percentage of NK cells than T cells can produce IFN-gamma although differences can be identified within the NK cells subset in terms of IFN-gamma production. The production of IFN-gamma is fully achievable in the HIV(+) subjects, which is consistent with their elevated plasmatic levels of the cytokine. The possibility that NK cells that produce interferon gamma could represent a functionally distinct population committed to the production of this cytokine, is discussed.

Reversal of human immunodeficiency virus type 1 protein-induced inhibition of natural killer cell activity by alpha interferon and interleukin-2

A recombinant fusion peptide, Env-Gag, derived from the human immunodeficiency virus type 1 (HIV-1) genome corresponding to a defined portion of the envelope (Env) and internal core (Gag) proteins was examined for immunoregulatory effects on the cytotoxic activity of natural killer (NK) cell-enriched, large granular lymphocytes (LGL) from healthy donors. Percoll-separated, NK cell-enriched LGL precultured for 24 h with Env-Gag at 10- and 50-ng/ml concentrations, which significantly stimulated lymphocyte proliferation, caused significant suppression of NK cell activity. Denatured Env-Gag did not cause any effect on the NK cell activity of LGL. Two other control peptides, one derived from the Escherichia coli vector used to clone the HIV Env-Gag fusion peptide and the other derived from a non-HIV-1 viral antigen (rubeola virus), did not produce any observable effect on the NK cell activity of LGL, demonstrating the specificity of the effect produced by Env-Gag. Subsequent treatment of LGL with alpha interferon (IFN-alpha) or interleukin 2 (IL-2) alone partially reversed the Env-Gag-induced suppression of NK cell activity. However, LGL treated with both IFN-alpha and IL-2 completely reversed the suppression of NK cell cytotoxicity by Env-Gag. The combined effect of IFN-alpha and IL-2 in enhancing NK cell activity may provide a novel therapeutic approach to the restoration of depressed NK cell activity observed in HIV-infected patients.

Disease progression in HIV-positive women with moderate to severe immunosuppression: the role of depression. Dana Consortium on Therapy for HIV Dementia and Related Cognitive Disorders

Thirty-seven HIV-positive women were recruited in a 2-year prospective investigation into the role of depression in HIV disease progression. All participants had CD4+ cell counts of 200 or less at baseline and at least 3 CD4+ cell counts during follow-up. Participants were evaluated semiannually for CD4+ lymphocyte counts, B2Microglobulin (B2M), hemoglobin data, and new AIDS-defining illnesses. The Center for Epidemiologic Studies Depression Scale was used to assess for depressed mood. Over time, average rates of change in CD4+ counts did not differ significantly between depressed and nondepressed women, even after adjustment for age, antiretroviral use, and baseline CD4 count, and depressed women did not differ from nondepressed women in numbers of new AIDS-defining illnesses. The authors concluded that depression may not be a significant determinant of disease progression in women with advanced disease and called for further investigations with larger samples and women at earlier stages of the infection.

Expression of killer inhibitory receptors on cytotoxic cells from HIV-1-infected individuals

Dysfunction of cytotoxic activity of T and natural killer (NK) lymphocytes is a main immunological feature in patients with AIDS, but its basis are not well understood. It has been recently described that T and NK cell-mediated cytotoxicity can be regulated by HLA killer inhibitory receptors (KIR). In this work, we have determined on cytotoxic T cells and NK cells from HIV-1-infected individuals the expression of the following KIR molecules: p58, p70, and ILT2 (immunoglobulin-like family KIR) as well as CD94 and NKG2A (C-lectin-type family KIR). With some exceptions, no significant changes were found on the expression of immunoglobulin-like KIR in either CD8+ or CD56+ cells. Interestingly, the percentages of CD8+ and CD56+ cells expressing CD94 were significantly increased in these individuals. We also show that, in vitro, IL-10 up-regulates CD94 expression on CD8+ and CD56+ cells obtained from normal individuals, suggesting that the augmented expression observed in HIV-infected individuals could be related to the high levels of IL-10 previously described in HIV-1-infected individuals.

Intracerebral interleukin-1beta impairs response to tumor invasion: involvement of adrenal catecholamines

Interleukin-1beta (IL-1beta) is released within the brain following stress, trauma, infection, and in specific brain disorders. This centrally acting IL-1beta has recently been shown to impair peripheral immunity. Central administration of IL-1beta suppresses natural killer (NK) cell activity impairs lung clearance of tumor cells and enhances tumor colonization. Using an in vivo model of tumor colonization (lung clearance of NK-sensitive MADB106 adenocarcinoma cells), this study examined the role of the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS) in mediating these effects. We demonstrate that adrenalectomy significantly attenuated the impaired lung clearance of MADB106 tumor cells induced by intracerebroventricular (i.c.v.) administration of IL-1beta (20 ng). Supplementing adrenalectomized animals with corticosterone did not reinstate the effect. The effect of IL-1beta on lung clearance was blocked by pretreatment with the beta-adrenergic antagonist, nadolol (0.5 mg/kg), but not by the alpha-antagonist phentolamine (5 mg/kg). Peripheral noradrenergic pathways are not implicated given that systemic administration of the noradrenergic neurotoxin, 6-hydroxydopamine, did not block the effect of IL-1beta. Taken together, these findings indicate that IL-1beta impairs lung clearance of MADB106 tumor cells via the actions of adrenal catecholamines, most likely epinephrine, acting at beta-adrenergic receptors in the periphery.

HIV-1 Tat Inhibits Human Natural Killer Cell Function by Blocking L-Type Calcium Channels

Herein we show that functional phenylalkylamine-sensitive L-type calcium channels are expressed by human NK cells and are involved in the killing of tumor targets. Blocking of these channels by phenylalkylamine drugs does not affect effector/target cell binding but inhibits the release of serine esterases responsible for cytotoxicity. Interestingly, treatment of NK cells with HIV-1 Tat, which is known to affect several calcium-mediated events in immune cells, impairs their cytotoxic activity. In addition, Tat inhibits the rise in intracellular free calcium concentration upon cross-linking of the adhesion molecule CD11a, engaged during effector/target cell interaction, and the activation molecule CD16. Exogenous Tat does not influence NK-target cell binding but prevents NK cell degranulation. We propose that the molecular structure(s) on NK cells mediating the inhibitory effects HIV-1 Tat belong to L-type calcium channels, based on three lines of evidence: 1) binding of phenylalkylamine derivatives to these channels is cross-inhibited by Tat; 2) L-type calcium channels from NK cell lysates bind to Tat linked to Sepharose columns; 3) the inhibitory effect of HIV-1 Tat on NK cell function is prevented by the agonist of L-type calcium channels, Bay K 8644. Altogether, these results suggest that exogenous Tat is deeply involved in the impairment of NK cell function during HIV-1 infection.

Acute and chronic effects of cocaine on the immune system and the possible link to AIDS

The pathogenesis of AIDS is a complex and prolonged process that is affected by a variety of cofactors, including the abuse of both intravenous and smoked (crack) cocaine. The exact mechanisms by which cocaine facilitates this disease are yet to be proven, but likely include a combination of increased risk due to cocaine-related social behaviours, a wide-ranging capacity for cocaine to suppress the immune system, and an effect of cocaine on the infectivity and replication of HIV. While sometimes contradictory, both human and animal studies document that cocaine alters the function of natural killer (NK) cells, T cells, neutrophils and macrophages, and alters the ability of these cells to secrete immunoregulatory cytokines. In addition to these effects on the immune system, cocaine also enhances the infectivity and/or replication of HIV when tested using human cells in vitro.

Intracerebral HIV glycoprotein (gp120) enhances tumor metastasis via centrally released interleukin-1

Infection with the human immunodeficiency virus (HIV) is associated with a high incidence of cancers. This relationship does not appear to be due to a direct effect of the virus, and may be mediated by neuroimmune interactions since the HIV glycoprotein, gp120, enters the brain soon after infection with HIV, and intracerebroventricular (i.c.v.) infusion of gp120 suppresses aspects of cellular and tumor immunity. It has been speculated that this suppression may be attributed to the release of interleukin-1 (IL-1) in the brain induced by gp120. Using an in vivo tumor model, we examined the effect of centrally administered gp120 on tumor metastasis and lung clearance of mammary adenocarcinoma (MADB106) tumor cells in rats, and the role played by brain IL-1 in mediating these effects. We demonstrate that central administration of gp120 (4 microg) significantly (p<0.05) increased the retention of tumor cells in the lungs and significantly (p<0.02) enhanced the development of tumor metastases. Central administration of IL-1beta (10 ng) also significantly (p<0.05) increased retention of tumor cells in the lungs. The effect of gp120 on lung retention of tumor cells was blocked by co-administration of alpha-melanocyte stimulating hormone (alpha-MSH, 20 ng), a hormone that blocks many of the biological effects of IL-1, or the IL-1 receptor antagonist (50 microg). Given that systemic administration of gp120 or IL-1beta had no effect on the retention of tumor cells in the lungs, these findings indicate that gp120-induced secretion of IL-1 within the brain most likely mediates the effects of gp120 on tumor metastasis. These findings suggest a possible neuroimmune mechanism to account for the increased incidence and aggressiveness of tumors in HIV-infected patients.

Enhancement of natural killer and antibody-dependent cytolytic activities of the peripheral blood mononuclear cells of HIV-infected patients by recombinant IL-15

Natural killer (NK) cells are an important subset of lymphocytes capable of killing virus-infected target cells without prior sensitization. HIV-infected individuals show impairment of their NK cell activity. Although the mechanism responsible for this defect remains unclear, NK cytotoxicity of lymphocytes from these individuals can be partially restored by interleukin (IL)-2. IL-15 is a recently discovered cytokine that shares many biologic activities with IL-2--for example, enhancement of NK activity. In this study, we investigated the effect of recombinant IL-15 (rIL-15) on the NK and antibody-dependent cellular cytotoxicity (ADCC) effector activities of peripheral blood mononuclear cells (PBMCs) from HIV-infected individuals using K562 cell line and HIV gp120-expressing cells. The effect of anti-IL-15 antibodies on NK activity was also examined using PBMCs of HIV-seronegative individuals. Our results show that NK and ADCC activities of PBMCs in HIV-seropositive patients were significantly lower than those of seronegative donors (p < or = 0.05). However, these two activities were significantly enhanced when rIL-15 was added to the assay wells (p < or = 0.05). Moreover, addition of saturating concentrations of neutralizing monoclonal antibodies (mAb) specific for IL-2, IL-12, or interferon (IFN)-gamma in the assays failed to inhibit IL-15-mediated enhancement of NK cell functions. Only the antibody against IL-15 abrogated the upregulation of NK and ADCC activities mediated by IL-15, suggesting that this cytokine enhances NK cell functions through a mechanism that is independent of the induction of other cytokines. IL-15 did not exert any modulatory effect on the expression of CD16 or CD56 molecules. Our results show that IL-15 can increase the NK and ADCC activities of the PBMCs of HIV-infected individuals in vitro. In view of its higher therapeutic index as determined using murine models, IL-15 may represent a better immunotherapeutic agent than IL-2 to restore these functions in HIV-seropositive patients.

Antiviral activity of biological response modifiers in a murine model of AIDS. Requirement for augmentation of natural killer cell activity and synergy with oral AZT

We employed the Rauscher murine leukemia virus (RMuLV) as a murine retrovirus model of AIDS, to test biological response modifiers (BRM) and antiviral agents for potential therapeutic activity against the human immunodeficiency virus (HIV). We examined the relationship between the augmentation of natural killer (NK) cell activity and antiviral efficacy of a series of BRM, most of which are known inducers of interferon, in this model. Poly [I,C]-LC, MVE-2, and CL 246,738, but not Ampligen, soluble glucan, or 7-thia-8-oxoguanosine, consistently produced antiviral activity. In addition, the combination of suboptimal doses of oral 3'-azido-3'-deoxythymidine (AZT) (in drinking water) and poly [I,C]-LC produced a synergistic antiviral effect. With all the BRM tested, a consistent pattern emerged, namely that antiviral activity always correlated with the augmentation of splenic NK cell activity in infected animals. For instance, poly [I,C]-LC boosted NK activity much more in infected mice treated therapeutically (treatment initiated after infection) than prophylactically (treatment initiated before infection), and it had greater antiviral activity therapeutically than prophylactically. For the BRM tested, antiviral activity did not occur without augmentation of NK activity in infected mice. In contrast, augmentation of NK activity in uninfected mice bore no relationship to antiviral activity. Furthermore, elimination of NK cells by treating mice with anti-asialo GM1 abolished the antiviral activity of poly [I,C]-LC. Although splenic NK activity was ablated by anti-asialo GM1, serum interferon levels were not affected by this treatment. These results point to a causal connection between the augmentation of NK cell activity and the antiviral efficacy of these BRM in this murine AIDS model. NK cells thus appear to play a key role in resistance to this retrovirus, as has been suggested for HIV.

Characterization of natural killer and antibody-dependent cellular cytotoxicity of preterm infants against human immunodeficiency virus-infected cells

The odds risk of vertical transmission of human immunodeficiency virus (HIV) to preterm infants is almost four times that of term infants and may relate to maternal and neonatal factors. We characterized the competence of early nonspecific cellular immunity, namely natural killer cytotoxicity (NKC) and antibody-dependent cellular cytotoxicity (ADCC), of peripheral blood mononuclear cells (PBMC) from preterm (n = 20) and term neonates (n = 28) versus adult controls against a T cell line infected with the human T cell lymphotrophic virus-III(B) using a chromium-51 release assay. PBMC from term neonates exhibited levels of NKC activity equal to adults against HIV-infected targets, yet the NKC capacity of preterm neonatal PBMC was significantly diminished. The ADCC activity of both term and preterm neonatal PBMC against HIV-infected targets was significantly less than that of adult PBMC. Overnight stimulation of a subset of samples with IL-12 augmented the NKC activity of both infant groups and adults, whereas the ADCC activity remained unchanged. These findings demonstrate that term neonates are deficient in ADCC against HIV-infected targets, whereas preterm infants are deficient in both NKC and ADCC, which may relate, in part, to the increased risk of transmission of HIV with preterm delivery. In addition, IL-12 has the potential to augment both term and preterm neonatal antiviral defense.

Interleukin-2 and human immunodeficiency virus infection: pathogenic mechanisms and potential for immunologic enhancement

A hallmark of human immunodeficiency virus (HIV) infection is the progressive loss of CD4+ T lymphocytes; however, qualitative defects in immune responses occur prior to the precipitous drop CD4+ T cell numbers. One of the first immunologic defects to be described in HIV-infected individuals is a deficiency in interleukin (IL)-2 production. The addition of IL-2 in vitro to cultures of mononuclear cells from HIV-infected individuals partially or completely restored certain defective cellular immune responses. However, production of or addition of IL-2 has also been associated with increased viral replication in infected T cells. These observations underscore the pernicious correlation between immune activation and HIV replication. However, recent in vitro and in vivo studies have provided promising preliminary results suggesting that, at least at certain stages of disease, the benefits of IL-2 mediated immune enhancement may outweigh or override the inductive effects of this cytokine on HIV production.

Immunological and virological markers of HIV-disease progression

This review, based upon scientific literature, evaluates a number of immunological and virological markers for their usefulness as prognostic indicators for progression of HIV disease. The most widely studied marker, the CD4 positive T lymphocyte count, is perhaps the best single indicator of stage of illness. Serum factors such as neopterin and beta-2 microglobulin, alone and in combination with CD4 cell counts, have been shown to have good predictive value. Measurement of viral burden by quantification of viral RNA levels in plasma and immune cells also holds promise for following disease progression. It is recommended that a combination of these factors be monitored in evaluating stage of illness and responses to therapy in HIV-infected persons.

Defective natural immunity: an early manifestation of human immunodeficiency virus infection

Cytotoxicity mediated by natural killer (NK) and lymphokine-activated killer (LAK) cells may be of significance in host defense against viral infections. This study included 347 patients infected with human immunodeficiency syndrome virus (HIV) type 1 and 110 controls. The NK cell activity, either unstimulated or stimulated with interferon-alpha (IFN-alpha) or interleukin-2 (IL-2), and the LAK cell activity were suppressed in patients, but the NK/LAK cell activity did not differ between patients with AIDS and patients without AIDS. However, the IFN-alpha-stimulated NK cell activity and LAK cell activity were reduced in patients with symptoms of HIV disease (CDCIV) when compared with asymptomatic patients (CDCII+III). When the data were analyzed by multiple linear regression, the percentage of CD4+ cells had a positive effect on these two parameters in patients without AIDS, whereas the percentage of CD4+ cells had no significant effect on unstimulated and IL-2-stimulated NK cell activity in these patients. In controls and AIDS patients, the percentage of CD4+ cells had no effect on NK/LAK cell activity in multiple linear models. The total number of CD16+ cells was low in patients compared to controls, whereas the percentages of CD16+, CD56+, and CD16+CD56+ were either normal or elevated. Therefore, the decrease in NK cell subpopulations did not contribute to the observed depression in NK/LAK cell activity in vitro. It is concluded that natural immunity is suppressed in HIV-seropositive patients primarily because of a qualitative defect of the NK/LAK cells. This qualitative defect includes a reduced responsiveness to IFN-alpha, which is progressive until the onset of symptoms, and possibly related to the loss of CD4+ cells.

Natural killer suppressor factors in sera from HIV-infected subjects

We investigated the presence of NK suppressor factors in HIV+ sera. We further investigated if gp120 could be one of the substances responsible for the impairment of NKC regulation found in HIV+ asymptomatic patients. Our results indicate that HIV+ sera inhibit significantly normal NKC in a dose-dependent way, even at concentrations as low as 1%. The inhibitory effect of HIV+ sera decreased, but was not completely removed, by adsorptions of IgG or by treatment with a MoAb against human FcIgG. Pretreatment of normal effector cells with anti-CD16 MoAb slightly reduced their cytotoxic capability, but did not modify the suppressor effect of HIV+ sera. The The preincubation of normal PBMC with recombinant gp120 had also a suppressor effect even at 10 ng/ml. Pretreatment of HIV+ sera with anti-gp120 or anti-FcIgG MoAb reduced, but not completely, their inhibitory effect. In conclusion, HIV+ serum has a dose-dependent inhibitory effect on normal NKC. Most of this inhibition is caused by IgG, but other substances, such as gp120, can also contribute to it. Since the removal of IgG and further treatments of HIV+ sera were not able to abrogate completely the NK suppression, other serum factors still undetermined (TNF-alpha, other cytokines), should be considered.

Defective natural killer cell cytotoxic activity in feline immunodeficiency virus-infected cats

Flow cytometry has been employed to study NK cell cytotoxic activity in cats infected with feline immunodeficiency virus. The results show that animals infected for 12 months or more have decreased levels of NK cell cytotoxic activity in their blood. The impairment could not be overcome by in vitro treatment of effector cells with interleukin 2. Additional results suggest that the NK cells of infected cats are defective, in that they are still able to bind to target cells but have a reduced ability to kill them.

Psychology, immunology, and HIV

The interdisciplinary field of psychoneuroimmunology (PNI), which aims to clarify the relationship between psychological factors and immunity, can also play a role in our understanding of individual susceptibility to, progression of immunologically mediated disease. Mechanisms proposed to account for the profoundly damaging effects of human immunodeficiency virus (HIV) on immune function do only partially explain the variability in individual rates of progression, suggesting, therefore, that other immunomodulatory factors are also involved. Studies have examined the proposal that the effects of stress and HIV may interact in some complex way, and psychological, physiological and virological evidence for the role of stress in HIV progression is discussed in detail. A critical review of HIV-specific research in PNI, which can be broadly divided into cross-sectional, longitudinal, and intervention studies, and studies of long-term survivors, reveals that the relationship between stress and HIV progression remains equivocal, because of limitations due to methodological difficulties and to our inadequate understanding of immunology and HIV. A model is proposed for the influence of psychosocial stress on progression in HIV disease, which takes account of some of these difficulties.

Analysis of the cytolytic activity mediated by natural killer cells from acquired immunodeficiency syndrome patients in response to phytohemagglutinin or anti-CD16 monoclonal antibody

The aim of this study was to assess the cytolytic potential of natural killer (NK) cells from human immunodeficiency virus type 1 (HIV-1)-infected patients, at different stages of the disease. Twenty HIV-1 seronegative donors as well as sixty HIV-1 seropositive patients were studied. Phytohemagglutinin and/or the anti-CD16 monoclonal antibody Kd1 were used to redirect the peripheral blood lymphocyte lysis of these patients to the 51Cr-labeled Fc gamma receptor-positive P815 murine mastocytoma target cell line. In parallel, NK cytotoxicity to tumor targets was investigated. Seronegative as well as HIV-1 Center for Disease Control (CDC) stage II patients showed maintained cytolytic activity. The cytolytic potential declined with disease progression, starting with CDC IVC2 patients, and was strongly diminished in acquired immunodeficiency syndrome stage patients. This defect was accompanied by decreased cytolytic activity to tumor targets and was not corrected by the in vitro addition of interleukin-2. The number of cells bearing a mature NK phenotype was normal in all the study groups. Our data suggest that the impaired NK cytotoxicity to tumor targets described during the progression of HIV-1 disease may be related to the progressive loss of function of surface receptors involved in NK cell triggering.

Natural killer cell stimulatory factor (NKSF)/IL-12 and cytolytic activities of PBL/NK cells from human immunodeficiency virus type-1 infected patients

The aim of this study was to assess the effect of natural killer stimulatory factor (NKSF)/IL-12) on the cytolytic potential of natural killer (NK) cells from normal donors or HIV-1 infected individuals, at different stages of disease. The results obtained confirm the powerful ability of IL-12 to enhance PBLs' cytotoxic activity to tumour cells in normals and in those HIV-1 infected patients, with maintained cytotoxic activity. IL-12 was however poorly effective in enhancing the cytolytic potential of any donors. Similar results were obtained adding IL-2, even at doses as high as 100 IU/ml in patients with CD4 number below 200/mm3. These results should be taken into account when designing therapeutic trials of HIV-1 infection based on cytokines.

Circadian rhythms of circulating NK cells in healthy and human immunodeficiency virus-infected men

Antiviral immunity involves NK cells, which circulate rhythmically every 24 hours. We have investigated circadian and 12-hour rhythms in the peripheral count of circulating NK cells in 15 men infected with human immunodeficiency virus (HIV) and 13 healthy controls. We analyzed three phenotypes using double-labeling with monoclonal antibodies and flow cytometry assessment: CD3- CD16+, CD3-CD57+, and CD2+CD3-. A statistical validation of time-dependent differences was achieved if significance (p < 0.05) was validated both with analysis of variance and cosinor. The circadian rhythm had a similar asymmetric waveform for the three phenotypes and is homogeneous on an individual basis. The circulating NK cell count peaked in the early morning and was low at night. A circadian rhythm and a circahemidian harmonic characterized all phenotypes in healthy subjects. We considered two groups of HIV-infected men: those who were asymptomatic (eight) and those with acquired immune deficiency syndrome (AIDS) (seven). Circadian changes in NK cell count were similar in both subgroups and in healthy controls. The circadian pattern was also consistent among individual patients. Asymptomatic HIV-infected men (early-stage disease) exhibited more pronounced 12-hour rhythmicity than did patients with AIDS or controls. The circulation of NK cells does not appear to share the same synchronizer(s) as other circulating T- or B-lymphocyte subsets. Thus, HIV infection gradually abolished circadian rhythmicity in circulating T and B cells, whereas it did not disturb that in NK cells.

Natural killer-cell function in hemodialysis patients: effect of the dialysis membrane

Natural killer (NK) cells are specific peripheral blood lymphocytes which are involved in the lysis of malignant and virally transformed cells. In a prospective study of eight hemodialysis patients, we investigated the effects of recurrent exposure to the cuprophane (CU) membrane on the number and functional ability of NK cells, against both their classical in vitro target, K562 cell line, as well as the beta 2m/HLA negative cells that emerge during dialysis with CU membrane. The percent of NK cells, defined by the CD56 epitope, increased from 27.7 +/- 7.9% of cells at baseline to 59.2 +/- 12.0% after two weeks of dialysis with new CU membrane (P < 0.01). The ability of these cells to lyse K562 cells decreased from 28.7 +/- 16.5% at baseline to 12.5 +/- 6.2% (P < 0.001) after two weeks of dialysis with CU membrane, while their cytotoxicity against beta 2m negative cells increased during the same period from 32.5 +/- 12.4% to 61.3 +/- 23.7% (P < 0.001). These results are consistent with the observation that the cytolytic ability of NK cells is inversely related to target cell expression of HLA antigens and beta 2m expression on cell surfaces. In addition, the results of these studies confirm in vitro observations of the decrease in cytolytic activity of the NK cells when exposed to the CU membrane, and may explain the emergence of these beta 2m/HLA negative cells during dialysis with CU membrane. It is possible that these observations may also have a clinical relevance to the immune defects and increased incidence of malignancy in uremia.