The distribution of protein kinase C in human leukocytes is altered in microgravity.

Protein kinase C (PKC) is an ubiquitous enzyme that mediates intracellular signal transduction in eukaryotes. Jurkat and U937 cells were exposed to microgravity during a Space Shuttle flight and stimulated with a radiolabeled phorbol ester (3H-PDBu) that specifically activates and labels several PKC isoforms. Both the total amount of 3H-PDBu labeling per cell and the relative distribution of labeling between subcellular compartments were altered in microgravity compared to onboard and ground 1 g control samples. The amount of total phorbol ester labeling per cell was increased approximately twofold in microgravity samples when compared with onboard 1 g samples for both cell lines. The subcellular distribution of PKC in the cytosol and nuclear fractions appeared to be correlated with the applied acceleration. In both cell types the relative amount of phorbol ester labeling in the nuclear fraction decreased with applied acceleration, whereas the labeling in cytosolic fraction increased with g level. No significant differences were observed between labeling levels in the membrane fraction in both cell types. Interleukin-1beta synthesis by U937 cells was markedly decreased in microgravity when compared to the onboard 1 g control, suggesting that the observed alterations in PKC distribution may have functional consequences. The results may have important implications for the effect of gravity on cellular signal transduction.

Use of bed rest and head-down tilt to simulate spaceflight-induce immune system changes.

Bed rest, both with and without head-down tilt, has been extensively used as an earth-bound analog to study physiologic effects mimicking those occurring in weightlessness during spaceflight. We have been able to show in six subjects that 4 weeks of head-down tilt bed rest induces a significant decrease in interleukin-2 secretion by PHA-stimulated T lymphocytes. Another study, lasting 113 days, with two subjects showed a decreased interleukin-2 receptor expression in PHA-stimulated peripheral blood mononuclear cells but a decreased interleukin-2 production in one subject only. Under the same conditions, interleukin-1 production was largely increased in both subjects. Several other immune parameters were also analyzed. Increased interleukin-1 production could contribute to bone mineral loss encountered during bed rest and decreased interleukin-2 secretion could play a role in the appearance of infectious diseases often observed during bed red.

In vitro interleukin-1 and 2 production and interleukin 2 receptor expression in the rhesus monkey.

Anti-human monoclonal antibodies were used to detect and quantify interleukins-1 and 2 and interleukin-2 receptor expression in peripheral blood mononuclear cells from a rhesus monkey. Interleukin-1 production could be induced by phorbol esters (PMA) and was potentiated by phytohemagglutinin (PHA). Interleukin-2 secretion could also be induced by the combination of PHA and PMA, but only weakly with PHA alone. Interleukin-2 receptor expression was present in a subpopulation of unstimulated lymphocytes and could be enhanced by PHA or PMA. These data show once again that the rhesus monkey immune system is cross-reactive with the human one and that rhesus macaque could be a good model to study interleukin therapy.

The Rhesus monkey as a model for testing the immunological effects of space flight.

The Rhesus monkey has been proposed as a model for the effects of space flight on immunity. In order to determine the feasibility of the use of the Rhesus monkey as a model, we studied the use of Rhesus monkey cells for immunological procedures that have been shown to be affected by space flight in both rodents and humans. We have shown that both lymph node cells and peripheral blood leukocytes can be stained with monoclonal antibodies to detect the following surface markers: CD4, CD-8, Ia and surface immunoglobulin. Also, the level of Ia antigen expression was increased by treatment of the cells with human interferon-gamma. In addition, cells were induced to produce interferons and interleukins. Isolated neutrophils also demonstrated increased oxidative burst. These data indicate that the Rhesus monkey will be a useful model for space flight studies of immunity.

Isolation and confinement as a model for spaceflight immune changes.

The immune system of astronauts is disturbed during and after spaceflight. This situation may result from stressors encountered during the flight (microgravity, radiation, psychological stress, or confinement) or from physiological changes (demineralization or fluid shift). Therefore, ground-based investigations should be designed to determine the effects of these factors on the immune system. Very little is known about the influence of confinement or isolation on immune reactions. However, interesting data exist from experiments with animals and humans under different conditions (submarines, antarctic expeditions, single-person cave isolation, and underwater diving). The question remains as to whether these results can be extrapolated to spaceflight. Therefore, investigations of humans under isolation conditions analogous to space missions have been performed by Russian and, more recently, European investigators. Such investigations are important for understanding the physiological and psychological disturbances that occur during long periods of confinement, especially when future lunar and martian missions are considered.

Interferon production by and leukocyte phenotyping of rhesus monkey lymph node and peripheral blood cells.

The ability of peripheral blood leukocytes to produce interferon-gamma (IFN-gamma) and be labeled with monoclonal antibodies against cell-surface markers was determined in this study. Both peripheral blood leukocytes and lymph node cells were able to produce IFN-gamma after challenge with mitogens. The rhesus monkey IFN-gamma was detectable by means of a biological assay but not by means of a radioimmunoassay for human IFN-gamma. Peripheral blood leukocytes and lymph node cells from rhesus monkeys (Macaca mulatta) were treated with fluoresceinated antibodies directed primarily against cell-surface antigens of humans. The degree of binding was determined by means of flow cytometry. Several of the anti-human antibodies did bind to the rhesus monkey peripheral blood leukocytes, as expected. In a novel study, the antibodies bound in a similar fashion to rhesus monkey lymph node cells. Binding of the antibodies was equivalent whether the cells came from inguinal or axillary lymph nodes. Rhesus monkey peripheral blood leukocytes incubated with recombinant human IFN-gamma showed enhanced expression of class II major histocompatibility complex antigens, as detected with anti-HLA-DR antibodies.

CD3-stimulated Jurkat T cells mediate IL-1 beta production in monocytic THP-1 cells. Role of LFA-1 molecule and participation of CD69 T cell antigen.

In this study we investigated the T cell signals required for monocyte activation. We used an in vitro co-culture system involving two human cell lines: Jurkat T cells and THP-1 monocytes. Monocyte activation was monitored by measuring IL-1 beta production, whereas IL-2 secretion reflected Jurkat activation. We showed that CD-3 -stimulated Jurkat cells delivered an IL-1-inductive signal to THP-1 cells through a cellular contact which was independent of THP-1 Fc receptors cross-linking. Stimulation of IL-1 beta production did not appear to require lymphokine secretion by T cell since a lymphokine defective mutant of Jurkat cell was able to deliver the stimulatory signal. The LFA-1 molecule was clearly shown to participate in the cooperation process, but its role was likely to be restricted to mediating initial adhesive interaction rather than to transducing the IL-1 -inductive signal. Interestingly, the co-culture stimulated by (Fab')2 fragments of CD3 mAb displayed an enhanced IL-1 beta production without any increase of IL-2 secretion. This result indicated that Jurkat cells could stimulate THP-1 cells even when they were only partially activated. The kinetics and conditions of IL-1 beta production called our attention to the early T cell activation antigen CD69. We then showed that CD69 mAb interfered with transmission of the IL-1 inductive signal (40-50% inhibition of IL-1 production). Our results are suggestive of a new role for CD69 molecule intervening in the T lymphocyte-dependent monocyte activation process.

European isolation and confinement study. Confinement and immune function.

During spaceflight, several unusual factors act on the physiology of the astronaut: weightlessness, radiation, confinement, isolation, living and working in a small group, workload, and anxiety. The resulting physiological changes are known to include alterations of the immune system. It is difficult to determine from observations on astronauts which space-related factor(s) are responsible for the immune changes. Studies of analogous environments on Earth have supplied only scarce information. Dedicated simulation studies provide a better tool, where some space-related stress factors (weightlessness, radiation) are absent, but others are or can be present: isolation and confinement, small group living, workload, and anxiety. A reduction in immune activity was found in bed rest studies and in long-term Soviet confinement experiments (after 90 days). In the ISEMSI confinement experiment (28 days), a tendency to immune activation (PHA-reactivity and interleukin-2 production) was observed in two out of six subjects. There is a need for further experiments, in which a large number of immunological parameters can be analyzed.

Effects of long duration spaceflight on human T lymphocyte and monocyte activity.

Experiments were performed on blood samples from 5 cosmonauts in order to investigate the effects of long duration spaceflight (26 to 166 days) on immune activity. The experiments were performed on cultured mononuclear cells purified from blood samples collected during the preflight period and 24 h after landing. The production of interleukin 2, which is the major cytokine involved in T lymphocyte proliferation, was found to be enhanced after flight in some individuals, whereas the ability of mitogen-stimulated cells to express interleukin 2 receptor was impaired 24 h after flight for two cosmonauts out of five. Normal interleukin 2 receptor expression was obtained in all cases when lymphocytes were directly activated by a protein kinase C activating phorbol ester. On the other hand, no significant changes were observed in interleukin 1 production by cultured peripheral blood mononuclear cells. Lastly, the distribution of T lymphocytes subsets was examined in peripheral blood sampled 24 h after landing and was found to be within normal values.

Inhibition of phorbol ester-induced cell activation in microgravity.

T lymphocytes and monocytes were exposed to microgravity and activated to produce interleukin 2 and interleukin 1, respectively. When Jurkat T cells were triggered with monoclonal antibodies directed against the CD3/T cell receptor complex in the presence of THP-1 monocytes used as accessory cells, cell-to-cell contacts took place in microgravity leading to normal production of interleukin 2 and interleukin 1, as compared to ground controls. In contrast, when cells were individually stimulated by soluble substances including a protein kinase C activating phorbol ester, the production of interleukin 1 and interleukin 2 was dramatically inhibited during microgravity exposure. This result indicates that microgravity may affect the cellular target of phorbol ester.

HTLV-I infection in French West Indies: a case-control study.

A case-control study was performed in Martinique, French West Indies, comparing 66 anti-p24 antibody carriers to 91 seronegative subjects for HTLV-I, matched for age and place of residence. The aim of our study was to identify factors associated with HTLV-I infection and to observe whether clinical examination and biological measurements would reveal any abnormalities among the seropositive subjects. We observed a predominance of females among seropositive subjects (74% compared to 59%, p less than 0.05), and a greater risk due to earlier blood transfusions (p less than 0.001). This survey revealed important differences between cases and controls regarding socioeconomic factors: cases had fewer luxuries or advantages (i.e. bathroom, toilets, refrigerator, telephone, p less than 0.01), were more corpulent (p less than 0.05), and more often widowed, divorced or separated (p less than 0.01) than the controls. Although the differences were not significant, the seropositive donors seemed to be less educated, and were from a lower socioprofessional class than the seronegative donors. With regard to clinical symptoms (infections, adenopathies, splenomegaly, hepatomegaly) and biological parameters (blood count; T-cell subsets, electrophoresis of protids, immunoglobulins, calcemia, antischistosomal antibody), seropositive subjects appeared to be healthy; no parameters, except for alpha 1 globulin (p less than 0.05) and monocytes (p less than 0.05), were found to be correlated with seropositivity; but these two parameters remained within their normal ranges. This study confirms blood transfusion as a risk factor. It underscored the importance of socioeconomic factors for seropositivity.

Stimulation of human interleukin 1 production and specific mRNA expression by microtubule-disrupting drugs.

The production of interleukin 1 (IL1), a pleiotropic monocyte-derived interleukin, can be induced in vitro by various stimuli. The present study shows that cytochalasins which inhibit actin filament polymerization in various cell types have no significant effect on IL1 production from human monocytic cells. On the contrary, microtubule disrupters such as colchicine, vinblastine, and vincristine dramatically potentiate (15- to 35-fold), in a dose-dependent fashion, cell-associated IL1 and to a lesser extent (2.5- to 7-fold) released IL1 in the myelomonocytic THP1 cell line and in adherent peripheral blood mononuclear cells. The enhancing effect of the drugs was blocked by actinomycin D and by cycloheximide and was accompanied by an increase of specific IL1 beta mRNA expression as measured by Northern blot analysis, thus indicating that these drugs act at a transcriptional or post-transcriptional IL1 gene expression level.

The conformation of the CD3 complex on T lymphocytes is modified by calcium ions.

While calcium ions are known to play a prominent role in signal transduction in the activation of T lymphocytes, its mechanism of action, target and function have not been elucidated. One crucial event in the calcium-dependent process is the activation of the CD3 complex, and this, too, is not understood. While studying the release of Ca2+ from intracellular stores by several monoclonal antibodies (mAb) against CD3, we found that one of them, mAb 141, was ineffective unless free Ca2+ was present in the external medium. By flow cytometric analysis of the binding of this mAb to Jurkat T cells and peripheral blood lymphocytes we showed that 141 does not recognize the CD3 complex when external Ca2+ is chelated by EGTA. The binding was restored by addition of Ca2+ but not Mg2+. Finally at least one subunit of the CD3 complex displayed a modified electrophoretic migration rate when immunoprecipitated by Leu-4 in the absence of external free Ca2+. These results suggest that the conformation of the CD3 complex depends on Ca2+, the epitope recognized by 141 being concealed at low Ca2+ concentration.

Detection of human IL-1 alpha and IL-1 beta at the subpicomolar level by colorimetric sandwich enzyme immunoassay.

Two separate convenient sandwich enzyme immunoassay methods were developed for measuring the production of the monokines interleukin-1 alpha (IL-1 alpha) and interleukin-1 beta (IL-1 beta) from peripheral blood mononuclear cells. Polyclonal antisera raised against the recombinant proteins and selected on the basis of their ability to neutralize IL-1-induced IL-2 secretion were used for coating microtiter plates or preparing peroxidase-Fab' conjugates. Both techniques were able to accurately and specifically detect monokines from various sources in the sub-picomolar range and were not influenced by compounds currently used for cell activation. A high molecular weight form of IL-1 beta was demonstrated under certain conditions and the two enzyme immunoassays were successfully applied to the detection of IL-1 alpha and IL-1 beta present in cell supernatants following stimulation with mitogenic or chemical agents.

Effect of hypertonicity and monensin on CD3/TCR surface expression in human T cells.

Pretreatment of T lymphocytes with anti-CD3 or anti-TCR mAb results in the disappearance of the T cell receptor complex (TCR/CD3) from the cell surface. The mechanisms of this down-regulation have not been fully elucidated. We demonstrate here that the modulation of the CD3/TCR complex can be completely inhibited by hypertonic medium, a condition known to block receptor-mediated endocytosis. Consequently, the sequestration of the CD3/TCR complex associated to relevant mAb in acid vesicles did not occur under hypertonicity condition. Moreover, monensin, which is known to interfere with receptor recycling, was found to amplify the CD3/TCR modulation induced by specific mAb and decrease the uptake of 125I-labeled anti-CD3/TCR mAb by T cells. We therefore propose that mAb-CD3/TCR complexes are internalized via coated pits by a receptor-mediated endocytosis and then transported to acid compartments. MAb are degraded in lysosomes during this process, whereas CD3/TCR molecules recycle back to cell surface.

Monoclonal antibody internalization and degradation during modulation of the CD3/T-cell receptor complex.

Although it is well known that the CD3/T-cell receptor (TCR) complex modulates from the surface of T cells upon exposure to monoclonal antibodies (mAb) directed against it, the fate of bound mAb has not been yet elucidated. We therefore perform direct binding experiments of 125I-labeled mAb against CD3 or TCR to investigate their fate in Jurkat T cells. We demonstrated that all mAb were progressively internalized and degraded in Jurkat T cells and that this degradation was inhibited by chloroquine, an inhibitor of lysosomal degradation enzymes. The sequestration of anti-CD3 mAb in acid compartments was furthermore shown using cytofluorometry. All together our results show that antibodies against CD3 or against TCR follow the same endocytic pathway.

IL2-like material is present in human placenta and amnion.

Human term placenta was shown to react with different polyclonal and monoclonal anti-interleukin 2 (IL2) antibodies by using indirect immunofluorescence on frozen sections. Labelling was localized on syncytiotrophoblast membrane, amniotic epithelium and cytotrophoblast of the reactivity [corrected]. The reproducibility of the observations with different basal plate. These features were observed with two different rabbit anti-IL2 polyclonal antibodies, a sheep IL2 antiserum and 15.2, an anti-IL2 monoclonal antibody. However, DMS-1, a second anti-IL2 monoclonal antibody, did not react. Pre-incubation of anti-IL2 sera with IL2 resulted in the disappearance of syncytiotrophoblast reactivity. The reproducibility of the observations with different reagents strongly suggests that the recognized molecule shares several epitopes with IL2. However, it has not been possible to demonstrate the presence of a conventional IL2 receptor by using two monoclonal antibodies directed to the 55 kDa chain of IL2 receptor.