HIV vaccines: a brief overview.

The scope of the article is to review the different approaches that have been used for HIV vaccines. The review is based on articles retrieved by PubMed and clinical trials from 1990 up to date. The article discusses virus complexity, protective and non-protective immune responses against the virus, and the most important approaches for HIV vaccine development.

Increased lipid peroxidation and abnormal fatty acid profiles in seminal and blood plasma of normozoospermic males from infertile couples.

BACKGROUND: Reactive oxygen species (ROS) are essential for sperm function. However, excessive ROS production can impair sperm function and might be a factor contributing to male infertility. METHODS: We investigated the levels of arachidonic acid (AA) and docosahexaenoic acid (DHA) as well as lipid peroxidation, as represented by thiobarbituric acid reactive species (TBARS), in blood and seminal plasma of 38 normozoospermic males from infertile couples (NSI-males), compared with that of 17 fertile volunteers (FV-males). RESULTS: TBARS levels in blood and seminal plasma were higher in NSI-males than in FV-males (P < 0.0002, P < 0.0003, respectively), as were AA levels (P < 0.0003, P < 0.00004, respectively). On the contrary, the blood and seminal plasma levels of DHA were lower in NSI-males than in FV-males (P < 0.02 and P < 0.05, respectively). The AA/DHA ratios in blood and seminal plasma were higher in NSI-males than in FV-males (P < 0.003, P < 0.0007, respectively). Significant correlations between seminal and blood plasma levels of TBARS (P < 0.0001, r = 0.548), AA (P < 0.0001, r = 0.571) and DHA (P < 0.0001, r = 0.506) were found. CONCLUSIONS: Our data provide new insight into lipid metabolism in male infertility and indicate that systemic oxidative stress resulting in increased lipid peroxidation and an altered fatty acid profile may be, at least in part, responsible for infertility even in normozoospermic males.

Inflammation and nitric oxide production in skeletal muscle of type 2 diabetic patients.

An inflammatory process may be involved in nitric oxide production in skeletal muscle of type 2 diabetic patients. Nitric oxide generation in skeletal muscle was assessed in 14 non-complicated type 2 diabetic patients and in 12 healthy subjects. In samples of quadriceps femoris muscle, endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), nitrite, nitrate and nitrotyrosine were determined. The macrophage-specific antigen CD163, the T-cell membrane factor CD154 and tumour necrosis factor-alpha (TNF-alpha) were also assayed. In six patients, ultrastructural analysis of muscle was performed. Nitrites and nitrates were increased in patients as compared to controls (22.7+/-4.5 and 32.7+/-7.0 vs 16.0+/-2.9 and 22.8+/-4.0 micromol/mg protein; P<0.001, Mann-Whitney U test). Endothelial NOS was similar in diabetic and control subjects (36.4+/-13.8 vs 36.3+/-6.8 ng/mg protein), contrasting with the significant increase of iNOS recorded in patients (34.3+/-13.0 vs 8.5+/-2.8 ng/mg protein, P<0.00002). Nitrotyrosine levels were higher in the patient than in the control group (42.1+/-24.4 vs 10.3+/-2.5 ng/mg protein, P<0.00002), as were CD163 (10-fold) and TNF-alpha (fourfold) levels. Furthermore, CD154 levels were detectable only in the patient samples (10.2+/-5.3 ng/mg protein). By multiple-regression analysis, changes in glycated haemoglobin values could predict 96% variation in nitrotyrosine. Macrophages were present in all muscle samples analysed by electromicroscopy. The increased levels of CD163, CD154 and TNF-alpha indicate that an inflammatory process occurs in skeletal muscle of type 2 diabetic patients. This may contribute to iNOS induction, muscle damage and insulin resistance.

Activity profile in multiple sclerosis: an integrative approach. A preliminary report.

In order to define an activity profile in patients with multiple sclerosis (MS), T-cell subpopulations and proliferative responses to myelin basic protein (MBP) associated with anti-MBP antibodies, nitrotyrosine levels in serum and cerebrospinal fluid (CSF), and serum CD40L (sCD154) were simultaneously assessed in 29 consecutive and untreated MS patients. When compared to controls, patients in secondary progressive stable (SP/I), or in full remission (RR/I) stages, individuals with secondary progressive active disease (SPIA) or in acute relapse (RR/A) showed a significant decrease of CD4/CD45RA+ T cells associated with an increase of absolute numbers of CD4/45R0+ T cells (p < 0.001). In addition, in vitro-specific T-cell proliferative responses against MBP (SP/A, RR/A, SP/I: p < 0.001 versus controls) in association with augmented sCD154 serum levels (SP/A, RR/A, versus controls p < 0.001) and a significant increase of both CSF and serum levels of anti-MBP antibodies and nitrotyrosine levels (p < 0.001) were also found. Thus, the simultaneous evaluation of antibody and cell-mediated immunopathological parameters, along with the effector mediators of inflammation such as the nitric oxide products, offers a new integrative approach to characterize markers of clinical activity in MS patients, which may be used at the moment of the initial diagnosis and during an apparent recurrences of the disease to monitor therapeutic protocols and to determine whether immune-based nerve destruction mechanisms are still operating in patients with few clinical findings.

Antihypertensive treatment decreased serum leptin levels in severe preeclampsia during pregnancy.

BACKGROUND: Plasma leptin levels in preeclamptic patients have been reported to be similar compared to those of normotensive pregnant women. Nonetheless, no reports have dealt with the effect of antihypertensive treatment and leptin in preeclamptic patients. METHODS: The study involved three groups of a similar age, body mass index and weeks of gestation. The groups were 30 normal pregnant women and 23 pregnant women with severe preeclampsia (SPE). The SPE patients were not treated prior to admission and the treatment was a single dose of alpha-methyldopa or hydralazine alone or in combination. The samples were taken at random in the afternoon (isotonic saline or pharmacological treatment) and 1 h before and after the treatment was given. Leptin serum levels were determined by a commercial sandwich ELISA assay. RESULTS: Leptin levels of the SPE group prior to the treatment were similar to the levels recorded for the normal pregnant women. However, after 1 h leptin levels were significantly higher (p < 0.001) in the nontreated patients (8.0 +/- 1.5) compared with those treated (5.15 +/- 0.9). CONCLUSION: These marked differences between treated and nontreated patients suggest that leptin levels may be modulated by a single antihypertensive treatment in preeclamptic patients with a discrete increase in blood pressure.

Muscle fiber composition and capillarization in relation to metabolic alterations in hypertensive men.

The aim of this study was to determine if there is a relationship among skeletal muscle fiber composition, capillarization, blood pressure (BP) and/or the components of the metabolic syndrome. Two groups were compared: 8 recently diagnosed, untreated, hypertensive men (BP > or = 140/90) and 7 normotensive men as controls. Muscle biopsies were taken from the vastus lateralis part of quadriceps femoris muscle in order to assess: fiber type proportion, capillarization, hexokinase, citrate synthase, beta-hydroxyacyl CoA dehydrogenase activities; lipoprotein lipase mass and activity, free fatty acids and triglycerides. Serum levels of insulin, glucose, cholesterol, uric acid and triglycerides were also assayed. Hypertensive patients had higher insulin levels and insulin resistance [homeostasis model assessment (HOMA)], a decreased hexokinase activity and an increase of muscle lipoprotein lipase mass as compared to controls. Interestingly, correlations among values differ in each group. The percentage of type IIB fibers was related to diastolic BP (blood pressure) in control and to mean BP in hypertensive subjects. Serum cholesterol and glucose were inversely related to the percentage of type I fibers in the control subjects. Negative correlations between capillarization and glucose, cholesterol and uric acid levels were found in control subjects. In all subjects, a strong correlation was found between SBP (systolic BP) and DBP (diastolic BP), and insulin resistance (IR) and uric acid levels. Muscle fiber type proportion and capillarization were related to blood pressure and components of the metabolic syndrome.

Serum leptin levels in different types of hypertension during pregnancy.

We determined the serum levels of leptin in 96 pregnant women with body mass index between 20 to 30, 30 normal (NP), 26 with mild preeclampsia (MPE), 27 with severe preeclampsia (SPE), 6 with chronic hypertension plus preeclampsia (CHT+PE) and 7 with chronic hypertension (CHT). A significant (p < 0.01) decrease in leptin levels was observed in the SPE group when compared with the NP group. On the contrary, significant (p < 0.05) increases were observed in the CHT and CHT+PE groups when compared with the NP group. Leptin levels were significantly higher in the MPE (p < 0.001), CHT (p < 0.01) and CHT+PE (p < 0.5) groups when compared with the SPE. No significant differences were observed in the CHT group when compared with CHT+PE. Moreover, a positive correlation was encountered (r = 0.6, p < 0.001) between platelet number and leptin levels for all the patients with preeclampsia. These results suggest that leptin levels may be useful metabolic parameter in different types of hypertension during pregnancy.

Metabolic changes in DOCA-salt hypertensive rats.

In a previous report, we observed an altered proportion of fiber types and a reduction of capillary per fiber ratio in extensor digitorus longus (EDL) and soleus (SOL) muscles of deoxicorticosterone acetate (DOCA)-salt hypertensive rats when compared with controls. The aim of the present study was to ascertain various carbohydrate and lipid enzyme activities and substrates that may be involved in the morphological changes reported. In the SOL muscle of hypertensive rats, glucose, glycogen and triglycerides (TG) levels were increased, citrate synthase (CS) and beta-hydroxy-acyl-CoA dehydrogenase (HAD) activities were reduced, while hexokinase (HK) and lipoprotein lipase (LPL), LPL mass, lactate and free fatty acids (FFA) levels were unchanged. In EDL muscles of hypertensive rats, glycogen levels and LPL mass were higher than in controls, while CS, HAD, HK, and LPL activities and glucose, lactate, FFA and TG levels were unmodified. Serum levels of insulin, TG, cholesterol and FFA were increased while glucose levels were decreased and high-density lipoprotein-cholesterol levels were similar in hypertensive rats when compared with controls. In conclusion, hypertensive rats showed increased glycogen in both EDL and SOL muscles, with hyperinsulinemia and reduced glycemia. Hyperinsulinemia might have been a compensatory response to insulin resistance. The oxidative capacity of SOL muscle was reduced indicating that glucose uptake was conduced via non-oxidative metabolism. TG, FFA and cholesterol were increased in serum and TG in SOL muscle.

HCV RNA sequences in eosinophils of chronic HCV-infected patients.

In the present study we examined the presence of Hepatitis C virus (HCV) RNA sequences in eosinophils (Eos) isolated from 10 chronically HCV-infected patients. At the time of the study patients showed levels of alanine aminotransferase (ALT) and aspartate aminotranferase (AST) above the normal upper limits (129 IU/L +/- 77 and 56.2 IU/L +/- 40, respectively). Absolute and relative total leukocyte and Eos counts were within the normal range. Highly purified eosinophils (> 98 %) were obtained by Ficoll-Hypaque (d = 1.114 g/mL) and Percoll gradient centrifugation following by immunomagnetic absorbtion to cell specific antibodies. Mononuclear cells (MN) and neutrophils (Neu) were also purified from these patients. PCR analysis of these cell populations revealed the presence HCV RNA sequences in 4/10 Eos, 6/10 MN and 2/10 Neu cell samples. The results suggest that, in addition to MN and Neo cells, Eos might also be susceptible to HCV infection.

Expression of low-density lipoprotein receptors in peripheral blood and tonsil B lymphocytes.

B lymphocytes, purified from peripheral leucocytes from young normolipaemic humans, expressed and internalized low-density lipoprotein receptors (LDLR). The expression was assessed by a monoclonal anti-LDLR. The internalization of LDL was assessed by LDL labelled with 125I (125I-LDL) and 1,1'-dioctadecyl-3,3,3',3' tetramethyl-indocarboxycyanine perchlorate (LDL-DiI). The expression of LDLR, assessed by anti-LDLR, was: 38 +/- 8% (n = 5) for fresh purified cells, 60 +/- 10% (n = 12) for non-stimulated cells, 79 +/- 5% (n = 10) for IL-2 (100 U/ml)-stimulated cells and 95 +/- 5% (n = 8) for pokeweed mitogen (PWM) (1:200 dilution)-stimulated cells. The optimal concentrations of agonist were 100 U/ml of IL-2, and 1:200 dilution of PWM. IL-2 and PWM increased the internalization of LDL-DiI by 1.5-fold. The internalization of LDL-DiI was maximal at 60 microg of protein/ml (48 +/- 8%). Scatchard analysis revealed a Kd of 3.2 +/- 0.22 x 10(-8) M and 2180 +/- 190 binding sites in non-stimulated cells, a Kd of 7.73 +/- 0.36 x 10(-9) M and 12,500 +/- 430 binding sites for IL-2 (100 U/ml)-stimulated cells, and a Kd of 7.2 +/- 0.43 x 10(-9) M and 13,250 +/- 450 binding sites for PWM (1:200 dilution)-stimulated cells. Lineweaver-Burk analysis of LDL binding (LDL-DiI) revealed that the apparent Kd for non-stimulated cells was 1.3 +/- 0.11 x 10(-8) M, and 9.2 +/- 0.2 x 10(-9) M and 7.5 +/- 0.25 x 10(-9) M for IL-2- and PWM-stimulated cells, respectively. B lymphocytes from tonsils also showed a high expression of LDLR assessed with anti-LDLR (70 +/- 6%). The high expression of LDLR and the avid internalization of LDL suggest that LDL may be important for B cell physiological responses.

Increased peroxide production by polymorphonuclear cells of chronic hepatitis C virus-infected patients.

To evaluate the oxidative burst in hepatitis C virus (HCV) infection, intracellular hydrogen peroxide (H2O2) production of polymorphonuclear (PMN) cells isolated from 15 chronic HCV-infected patients and 11 controls was assessed by flow cytometry in a time kinetic. Under nonstimulated and phorbol myristate acetate (PMA)-stimulated conditions, H2O2 production was higher in HCV-infected patients than in controls (P <0.05) at the time points of 20, 30, and 40 min. A positive correlation between H2O2 production by PMA-stimulated cells and serum levels of alanine aminotransferase and aspartate aminotransferase was found in the HCV-infected patients (r = 0.877, P <0.01 and r = 0.9351, P <0.001, respectively). RT-PCR analysis of purified mononuclear (MN) and PMN cells from HCV-infected patients revealed the presence of HCV RNA in 60% of MN and 27% of PMN cell samples. These results suggest that a functional alteration of PMN cells is manifested in this chronic viral infection which may represent an additional factor in the development of liver lesions.

Characterization of local memory cells in stage-classified pulmonary tuberculosis: preliminary observations.

Immunophenotype analysis and proliferative responses were investigated in bronchoalveolar lavage (BAL) cells from 21 patients with stage-classified tuberculosis: six with localized pulmonary infiltrate (LPI); seven with diffuse pulmonary infiltrate (DPI); and eight with pleural effusions (PE). Bronchoalveolar lavage cells from these patients contained a high number of cells/ml. The macrophage number was significantly lower in the DPI group (P < 0.05) compared to the LPI or PE groups. Conversely, neutrophils were markedly increased in DPI patients compared to LPI (P < 0.01) and PE (P < 0.01) patients. Lymphocyte infiltration (97.7 +/- 2.3% CD3+, > 83% alphabeta+ and CD4+ > CD8+) was observed in the three groups. A significant increase in the number of total lymphocytes (P < 0.01) and CD4+ cells (P < 0.05) was observed in the LPI group compared to the PE group. In the LPI group CD4+CD45RO+ cell infiltration was higher than CD4+CD45RA+ cells (P < 0.001), contrasting to similar numbers of these subpopulations in the DPI group. Lymphocytes from three out of three LPI patients (alphabeta+CD4+CD45RO+) responded against tuberculin purified protein derivative contrasting to the unresponsiveness of five patients with either DPI or PE. This impaired response was reverted in two out of five patients by using peripheral blood monocytes instead of alveolar macrophages. It is suggested that, in humans, alphabetaCD4+CD45RO cells are the main lymphocyte type involved in the initial local cell-mediated immune response against Mycobacterium tuberculosis.

Impairment of natural killer (NK) cytotoxic activity in hepatitis C virus (HCV) infection.

In the present study, we evaluated the NK cell cytotoxic activity in a group of HCV-infected individuals. Although the number of NK cells present in the peripheral blood of the HCV-infected patients was comparable to non-infected individuals, spontaneous NK cytotoxicity was four-fold lower (P < 0.001) than in normal donors. This functional impairment was not overcome by depletion of adherent or B cells, and it was partially restored by short-term (18 h) stimulation with IL-2. However, long-term stimulation (72 h) with this lymphokine induced activated killer cell (LAK) activity comparable to normal controls. The reduction in NK cytotoxic response does not seem to be due to soluble suppressive factors, since incubation of normal peripheral blood mononuclear cells (PBMC) with infectious HCV serums for a 4-h period does not affect NK spontaneous cytotoxic activity. Successful in vitro infection of PBMC with HCV infectious serum also resulted in an impairment of NK cytotoxicity, suggesting that altered NK function is associated with HCV infection and may be responsible, at least in part, for the chronicity of the infection.

Secretion of cytokines by natural killer cells primed with interleukin-2 and stimulated with different lipoproteins.

Natural killer (NK) cells were shown to secrete differentially interleukins (IL), IL-1 alpha, IL-1 beta, IL-2, IL-8, interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), granulocyte-macrophage colony-stimulating factor (GM-CSF), and leukaemia inhibitory factor (LIF) upon stimulation with optimal concentrations of chylomicrons (CM), very-low-density lipoprotein (VLDL), low-density lipoprotein (LDL), high-density lipoprotein (HDL) or acetyl-modified low-density lipoprotein (AcLDL). CM, VLDL, LDL and AcLDL induced LIF secretion which was absent in nonstimulated cells. CM, VLDL, and LDL did not affect IL-1 alpha secretion. CM stimulated IL-8 > TNF-alpha > IL-1 alpha > IL-2 = IFN-gamma, and decreased seventeen-fold GM-CSF secretion. VLDL stimulated IL-8 secretion > IL-1 alpha = IL-2 > IFN-gamma > TNF-alpha and decreased fivefold GM-CSF secretion. LDL stimulated IL-8 secretion > IL-1 alpha > IL-2 = IFN-gamma, it did not modify TNF-alpha and inhibited five hundred-fold GM-CSF secretion. HDL stimulated IL-2 secretion = IFN-gamma > IL-8, it decreased GM-CSF secretion > IL-1 alpha > IL-1 beta > TNF-alpha without affecting LIF. AcLDL stimulated IL-8 secretion > TNF-alpha > IL-1 alpha > IL-2 = IFN-gamma = IL-1 beta, and decreased GM-CSF secretion eightfold. When NK cells were primed with 10, 100 or 500 IU/ml of IL-2 before the addition of lipoproteins, a decrease in the secretion of cytokines was observed as compared with cells primed with IL-2 only. Differences in cytokine secretion were observed among the diverse type of lipoproteins used for cell stimulus. Thus, lipoproteins may condition NK cytokine secretion and cell activation.

Low density lipoprotein receptor expression and function in human polymorphonuclear leucocytes.

Low density lipoprotein receptors (LDLR), capable of internalizing LDL, are expressed in polymorphonuclear neutrophils (PMN). The expression was assessed using anti-LDLR antibody by flow cytometry. The internalization of LDL was assessed by: (i) quantification of the uptake of labelled LDL with 1,1'-dioctadecyl-3,3,3',3' tetramethyl-indocarboxycyanine perchlorate (DiI) by flow cytometry; and (ii) the binding of LDL-125I. In fresh purified cells, Lineweaver Burk analysis of LDL binding (LDL-DiI) revealed that the calculated Kd (internalized LDL) for PMN (15.0 x 10(-9) M) is lower than the Kd for monocytes (1.1 x 10(-7) M) and the Kd for lymphocytes (3.2 x 10(-7) M). Scatchard analysis (LDL-125I) revealed 25,000 binding sites and a Kd of 9.6 x 10(-9) M for PMN. The interaction of LDL with its receptor caused a two-fold fast (peak at 1 min) and transient increase in the oxidative burst, measured by the formation of 2',7' dicholoflurescein (DCF) by flow cytometry. This effect was not observed in monocytes or lymphocytes, and it was blocked by anti-LDLR antibody. The stimulation of LDL was optimal at 10 microg of protein/ml. LDL was able to suppress DCF formation induced by phorbol myristate acetate (PMA) and PMA was unable to further stimulate LDL-treated cells, suggesting protein kinase-C (PKC) involvement in LDL effects. Using a PKC assay, LDL was shown to induce a two-fold increase in PKC translocation to the membrane. Thus, LDL increases PMN oxidative burst through a PKC-dependent pathway.

Nitric oxide in different types of hypertension during pregnancy.

1. Serum nitric oxide (NO) levels (determined by its products of oxidation) were assessed in non-pregnant women, normal pregnant women and patients suffering from mild pre-eclampsia (MPE), severe pre-eclampsia (SPE), chronic hypertension (CHT) and CHT with pre-eclampsia (CHT + PE). The levels of NO products were significantly reduced during pregnancy in MPE (P < 0.001), CHT + PE (P < 0.01) and SPE (P < 0.05). Significant reductions of NO products were also observed in puerperium (P < 0.001) in all groups except CHT + PE (P < 0.05). 2. In normal pregnancy, three events were related to NO levels: (1) negative correlations were found between the levels of nitrite (r = -0.73, P = 0.0003), nitrate (r = -0.53, P = 0.017) and the number of weeks of gestation; (2) in the caesarean section group, the levels of NO at puerperium were significantly lower (P < 0.05) than those during pregnancy; and (3) there was a significant reduction in NO levels in the pregnant women carrying male fetuses as compared with female fetuses (P < 0.05). 3. In SPE, the patients with a family history of hypertension had lower levels of NO compared with the patients without such a history (P < 0.05). 4. A negative correlation was observed between systolic blood pressure, diastolic blood pressure and NO levels in MPE (r = -0.62, P = 0.013 and r = -0.68, P = 0.0049 respectively) and SPE (r = -0.72, P = 0.004 and r = -0.53, P = 0.037 respectively). 5. In SPE, positive correlations were observed between platelet count and nitrite (r = 0.67, P = 0.006) and nitrate levels (r = 0.56, P = 0.028). 6. In MPE, patients with anti-hypertensive treatment showed significantly (P < 0.05) higher levels of NO compared with the non-treated patients. 7. NO may be important in the physiopathology of hypertension during pregnancy, although several factors may affect its levels.

Regulatory effects of lipoprotein lipase on proliferative and cytotoxic activity of NK cells.

Lipoprotein lipase (LPL) induced, in a dose-dependent fashion, a 2-fold and 11-fold increase in the proliferative response of peripheral blood lymphocytes (PBL) at 48 and 72 h, respectively; a 4- and 12-fold increase in natural killer (NK) cells, respectively; and a maximal 3-fold induction in interleukin-2 (IL-2)-treated NK cells at 72 h. T lymphocytes did not proliferate independently of the concentration of LPL used. LPL decreased the proliferative response of K562 and U937 cell lines. The effect on NK cells could be blocked by anti-LPL if it was added before LPL binding to the cell membrane. Contrary to its effects on NK proliferative response, LPL inhibited spontaneous cytotoxicity and lymphokine-activated killer activity (LAK). The effect was dose-dependent, target-dependent (U937 was more sensitive than K562 in LAK assays), but not LPL-binding time-dependent. Treatment of NK cells with heparinase overcame the inhibitory effect of LPL in spontaneous cytotoxicity. LPL binding to cell membranes, as assessed by flow cytometry, was as follows: K562 cells > monocytes > NK cells > LAK cells > U937 cells, absent in T lymphocytes and partially sensible to heparinase and IL-2 treatments. Protein kinase C translocation was observed upon treatment of NK cells with LPL. Three proteins in NK cell membrane (76, 57.2, and 27.2 kD), two in the cytosol (57.2 and 27.2 kD), and only one in ANA-1 cell membrane (76 kD) were precipitated with LPL-Sepharose. LPL receptors seem to be responsible for the proliferative and cytotoxic response observed in LPL-stimulated NK cells.

Expression and function of low-density lipoprotein receptors in CD3-CD16+CD56+ cells: effect of interleukin 2.

Low-density lipoprotein receptors (LDLR) have been shown to be expressed, internalized, and transcribed in CD3-CD16+CD56+ cells. Only a low percentage (up to 12%) of NK cells express LDLR. Interleukin 2 (IL-2) (1000 IU/ml) induced a threefold increase in the expression of LDLR on the cell surface that results from, at least in part, augmentation of LDLR turnover from the cytosol to the membrane. Scatchard analysis revealed that IL-2 decreased the Kd of LDLR binding for LDL from 7.53 to 4.33 nM with an increment in the number of binding sites from 2500 up to 5000. Both the proliferative response and cytotoxic functions of these cells are affected by LDL. Low concentrations of LDL induce an increase in the proliferative response (up to eightfold) and in the cytotoxic response of NK cells (up to fivefold). High concentration (more than 60 micrograms/ml) of LDL hampers both proliferative response and cytotoxic activity of NK cells. LDL did not affect the cytotoxic functions of IL-2-activated NK cells. Overall, we have shown that LDLR is expressed on the surface of NK cells and can be augmented by IL-2. Furthermore, we propose some insights into the mechanism responsible for the enhanced expression of LDLR on NK cell surface. In addition, our data clearly delineate that LDLR plays an important role in the regulation of proliferative responses and cytotoxic activity of these cells.

Expression of different lipoprotein receptors in natural killer cells and their effect on natural killer proliferative and cytotoxic activity.

Natural killer (NK) cells take up chylomicrons (CM), very low density (VLDL), low density (LDL), high density (HDL) and acetyl-modified low density (AcLDL) lipoproteins through different receptors, VLDL being the lipoprotein with the highest uptake and HDL the lowest. The uptake of LDL can be selectively blocked by the anti-LDL receptor, which does not affect the uptake of CM, VLDL, HDL and AcLDL. Although the uptake of lipoproteins assessed by flow cytometry using DiI is not very high, the lipoproteins are able to induce an increase in proliferative responses, VLDL, AcLDL and HDL being the most important ones with 12- and 17-fold increments, respectively. CM, VLDL and LDL at low concentrations increase NK cytotoxic activity, while HDL and AcLDL inhibit, in a dose-dependent fashion, the killing of NK cells against K562. These results suggest the presence of four different receptors that are responsible for the cytotoxic and proliferative responses observed.