The host response of CD28-deficient mice to Pneumocystis infection

Pneumocystis infection leads to a life threatening pneumonia in susceptible individuals. While depletion or dysfunction of CD4+T cells is a key determinant of susceptibility to Pneumocystis, the host response that leads to resolution of infection or lung injury is less well understood. We had previously shown that mice deficient in the T cell costimulatory molecule CD28 are susceptible to infection with Pneumocystis. A detailed analysis revealed that they clear Pneumocystis with delayed kinetics. This is associated with an influx of naïve CD8+ T cells. Depletion of CD8+ T cells did not alter organism burden, suggesting these cells are not responsible for clearance. Analysis of the cytokine milieu demonstrated a consistent increase in mRNA for IL-10 and IFN-gamma in the CD28-deficient mice. These data suggest that CD28 function in important in the efficiency of the host response to Pneumocystis pneumonia.

Requirement for CD28 in the effector phase of allergic airway inflammation

Central to the pathogenesis of allergic airway inflammation are the activation and differentiation of T lymphocytes. This process requires the participation of the CD28 costimulatory receptor. Blockade of CD28 has been demonstrated to prevent inflammation and airway hyperreactivity in a murine model of asthma. Whether this is due specifically to defects in initial T cell activation or whether effector responses are also impaired has not been determined. Using adoptive transfer studies of Ag-specific lymphocytes, we demonstrate that CD28 has a critical role in both the induction and effector phase of allergic airway inflammation. Transfer of in vitro activated and Th2-differentiated Ag-specific lymphocytes from wild-type hosts restored inflammation, but not tissue eosinophilia in CD28-deficient recipients. Furthermore, similarly activated and differentiated CD28-deficient lymphocytes were ineffective at mediating inflammation in wild-type recipients. Secondary cytokine and proliferative responses of activated Th2 cells were highly dependent on CD28 in vitro. Moreover, eosinophil recruitment to both the lung and peritoneum is impaired by the lack of CD28, suggesting a generalized defect in the ability of eosinophils to accumulate at sites of inflammation in vivo. These data identify a novel role for CD28 in the effector phase of allergic airway inflammation and suggest that inhibition of this pathway may be a useful therapeutic intervention in previously sensitized individuals.

T cell costimulatory molecule function determines susceptibility to infection with Pneumocystis carinii in mice

Loss of T cell number and function during HIV infection or secondary to pharmacologic immunosuppression renders individuals susceptible to opportunistic infections, including Pneumocystis carinii pneumonia. Because costimulatory receptors are critical for optimal T cell function, we hypothesized that these proteins would regulate susceptibility to opportunistic infections. We found that despite normal T cell numbers, mice deficient in the costimulatory molecules CD2 and CD28 spontaneously developed P. carinii pneumonia. In experiments using intratracheal injection of P. carinii organisms to induce infection, the loss of CD28 alone was sufficient to render mice susceptible to acute infection; however, the organism was eventually cleared. Examination of inflammatory responses to P. carinii revealed that mice deficient in both CD2 and CD28 accumulated CD8(+) T cells in their lungs in response to infection and demonstrated markedly reduced specific Ab titers. Analysis of cytokine profiles suggested that regulation of IL-10 and IL-15 may be important elements of the response to this pathogen. Thus, costimulatory molecule function is critical in determining the initial susceptibility to infection with P. carinii. Analysis of immunologic responses in these mice may provide important insights into the defects that render individuals susceptible to opportunistic infection, and provide opportunities for novel immunologically based therapies.

Polar redistribution of the sialoglycoprotein CD43: implications for T cell function

Contact between T cells and APCs results in the orchestrated segregation of molecules at the cell-cell interface and formation of a specialized structure termed the immunological synapse. This model predicts the topological seclusion of large molecules such as CD43 from the site of closest contact between the T cell and APC, allowing for the close apposition of cell membranes and effective TCR engagement. Similarly, during T cell migration segregation of CD43 to the uropod is thought to aid integrin adhesion at the leading edge of the cell by removing steric hindrance. We show in this work that CD43 distribution on T cells is regulated by a membrane proximal ezrin binding site and that failure to displace CD43 from the immunological synapse has no inhibitory effects on primary T cell activation. We also report that CD43 expression at the contact zone between T cells and matrix does not negatively regulate motility but may regulate LFA-1 de-adhesion. These results suggest that the steric barrier model of CD43 is inadequate and that alternative mechanisms account for the negative regulatory properties of CD43.

CD28 and CTLA4 Coordinately Regulate Airway Inflammatory Cell Recruitment and T-Helper Cell Differentiation after Inhaled Allergen

Airway inflammation after inhaled allergen exposure requires the recruitment, activation, and differentiation of antigen-specific T cells into T helper (Th) 2 effector cells. These processes are regulated not only by antigen engagement of the T-cell receptor, but also by specific accessory molecules on the surface of the T cell. We examined how the balance of signals derived through the CD28 and cytotoxic T-lymphocyte antigen (CTLA) 4 receptors modulate the outcome of inhaled antigen exposure in a murine model of allergic airway inflammation. Mice deficient in CD28 have defective Th2 cell development and failed to develop inflammation after sensitization and inhaled challenge with ovalbumin. Prevention of B7-CTLA4 interactions in CD28-deficient mice restored lymphocyte but not eosinophil recruitment to the airway. Analysis of cytokine gene expression revealed that T cells from CD28-deficient mice failed to differentiate into Th2 cells in either the presence or absence of B7-dependent signals, and therefore did not recruit eosinophils to the airway. Thus, the processes of T-cell recruitment to the airway and T-cell differentiation have distinct requirements for signals mediated through the CD28 and CTLA4 receptors, demonstrating that these receptors are important regulatory components in the development of allergic airway inflammation.

Cutting edge: distinct motifs within CD28 regulate T cell proliferation and induction of Bcl-XL

CD28 provides an important costimulatory signal in T cell activation that regulates multiple cellular processes including proliferation and survival. Several signal transduction pathways are activated by CD28; however, the precise biochemical mechanism by which CD28 regulates T cell function remains controversial. Retroviral gene transfer into primary T cells from TCR-transgenic, CD28-deficient mice was used to determine the specific sequences within CD28 that determine function. Discrete regions of the cytoplasmic domain of CD28 were identified that differentially regulate T cell proliferation and induction of the anti-apoptotic protein Bcl-X(L). Mutation of C-terminal proline residues abrogated the proliferative and cytokine regulatory features of CD28 costimulation while preserving Bcl-X(L) induction. Conversely, mutation of residues important in phosphatidylinositol 3-kinase activation partially inhibited proliferation but prevented induction of Bcl-X(L.) Thus the ability of CD28 to regulate proliferation and induction of Bcl-X(L) map to distinct motifs, suggesting independent signaling cascades modulate these biologic effects.

Coordinate regulation of T cell activation by CD2 and CD28

T cell activation requires co-engagement of the TCR with accessory and costimulatory molecules. However, the exact mechanism of costimulatory function is unknown. Mice lacking CD2 or CD28 show only mild deficits, demonstrating that neither protein is essential for T cell activation. In this paper we have generated mice lacking both CD2 and CD28. T cells from the double-deficient mice have a profound defect in activation by soluble anti-CD3 Ab and Ag, yet remain responsive to immobilized anti-CD3. This suggests that CD2 and CD28 may function together to facilitate interactions of the T cell and APC, allowing for efficient signal transduction through the TCR.

Serum erythropoietin titers during prolonged bedrest; relevance to the "anaemia" of space flight

The overall objective of these studies was to test the hypothesis that the suppression of erythropoiesis, which occurs during both spaceflight and bedrest, was mediated by reduction in circulating levels of erythropoietin. In each of two 7-day studies, groups of subjects were exposed to either horizontal or 6 degrees head-down tilt bedrest and no evidence was obtained to suggest that the erythropoietic effects were dependent on the angle of recumbency. An additional study involved six men who were exposed to horizontal bedrest for 28 days. Serum erythropoietin titers were not significantly depressed in any of the subjects but total red cell volume was decreased. Absolute increases in red cell numbers and reductions in plasma volume both elevate the haematocrit, but our data suggest that the mechanism of erythrosuppression in these two instances may be different.

Interactions of animal and computer models in investigations of the "anemia" of space flight

Previous studies in mice deprived of water have suggested that these animals, like men in space, show hemoconcentration due to plasma volume reductions, a weight loss greater than that due to fluid loss alone, and suppression of red blood cell production. To more fully understand the mechanisms responsible for the suppressed erythropoiesis in dehydrated mice, a mathematical model for erythropoietic regulation has been adapted to this rodent. Computer simulations suggested several new experimental studies to more fully understand the erythroid response to dehydration. The investigations were directed to determining whether dehydration was accompanied by: a) a shortened red blood cell survival, b) altered sensitivity of the erythropoietin (Ep)-producing mechanism, c) a shortened red blood cell transit time, d) changes in the Ep serum half-life, e) changes in hemoglobin P50, and f) reduced renal blood flow. All parameters except changes in renal blood flow were investigated in vivo and incorporated into, or omitted from, the mathematical simulations as directed by experimental findings. The mathematical model is able to realistically simulate the in vivo erythroid response to dehydration making only one, experimentally-untested, assumption. Computer simulations confirm conclusions drawn from the animal studies that the primary cause of the suppressed erythropoiesis in dehydrated mice is the reduced food intake, with hemoconcentration playing a relatively minor role. The interaction between computer simulations and animal experiments is shown to be a powerful approach for formulating and testing hypotheses, designing new experiments, and achieving a clearer understanding of the factors controlling erythropoiesis.

Electrolyte metabolism in rhesus monkeys with experimental salmonella sepsis

Prior investigations in the human indicate that alterations occur in electrolyte balance and serum concentration during infectious diseases. In order to explore these alterations in greater detail, electrolyte metabolism has been investigated in rhesus monkeys with a sublethal illness induced by intravenous inoculation with Salmonella typhimurium. The response to this illness was evaluated by a variety of measurements including serum and muscle electrolyte composition and renal function studies. In the animals with ad libitum dietary intake, a loss in muscle and serum potassium concentrations was evident within 24 h after inoculation. This was reflected in increased urinary potassium losses during the febrile phase of illness. Serum and muscle K concentrations returned to normal after 5 days of illness. Sodium and water content of muscle responded to infection in a more complex pattern. During the febrile phase, muscle sodium and water increased and sodium concentrations in serum and urine were elevated. During convalescence, renal retention of sodium was marked and overlapped the period of weight loss and the increased urine volume. This asynchrony in recovery of normal renal function appeared to be the cause of relatively large swings in plasma sodium concentrations during the early convalescent period. These investigations indicate that the altered serum concentrations in infectious diseases are the sum of renal and extrarenal factors controlling electrolyte metabolism, and that some of the most remarkable alterations occur during early convalescence as renal function returns to normal.

Dynamic regulation of erythropoiesis: a computer model of general applicability

A mathematical model for the control of erythropoiesis has been developed based on the balance between oxygen supply and demand at a renal oxygen detector which in turn controls erythropoietin release and red cell production. Tissue oxygen tension is regulated by adjustments of hemoglobin levels resulting from the output of a renal-bone marrow controller. Special consideration given to the determinants of tissue oxygenation included evaluation of the influence of blood flow, capillary diffusion, oxygen uptake, and oxygen-hemoglobin affinity. A theoretical analysis of the overall control system is presented including: a) dynamic and steady-state responses, b) sensitivity analysis to determine the relative importance of parameters and their influence on model behavior, c) properties of the model as a proportional controller, d) analysis of steady-state errors, and e) effectiveness of feedback regulation. Computer simulations of altitude hypoxia, descent from altitude, red cell infusion, and hemolytic anemia demonstrate the validity of the model for general human application.

Nuclear boundary detection algorithm based on a minimax derivative statistic for atypical bronchial squamous epithelial cells

The thresholding approach in scene segmentation of digitized cell images was found to be unreliable for use with squamous epithelial cells characterized by chromatin condensation within the nucleus. It was observed that the nuclear boundaries of such cells were visually distinguishable. An algorithm was developed for detecting nuclear boundaries in digitized cell images. This algorithm is based on a minimax derivative statistic that has maximum values at nuclear boundaries and low values elsewhere. The statistical properties of the confusion matrix of cellular scene segmentation are outlined. A measurement and a test statistic for scene segmentation errors based on those properties are presented.

Cell atypia profiles for bronchial epithelial cells: mathematical evaluation of sputum cellular atypia in squamous cell carcinogenesis of the lung

Atypical bronchial epithelial cells from the sputum of male cigarette smokers were digitized by scanning microphotometry and analyzed by computerized image analysis techniques. A set of specific analytic features based on cell morphology was extracted and combined mathematically to be expressed as a single number (Atypia Status Index). This index represented the stages of the cellular atypia (squamous metaplasia; mild, moderate or severe atypia; or carcinoma) quantiatively as a single number varying between 0.0 and 5.5 The Atypia Status Index for each cell correlated highly (94% to 99%) with visual cytopathologic classification. The distributions of cells according to their indices were profiled for patients at various stages of carcinogenesis and used to classify patients relative to their degree of cell atypia. These results compared favorable to those of the clinical evaluation.

Aytpia status index of respiratory cells: a measurement for the detection and monitoring of neoplastic changes in squamous cell carcinogenesis

A statistical procedure was developed for calculating an atypia status index (ASI) for cells from the bronchial mucosa. These indices represent the degree of abnormal changes in these cells and classify them as squamous metaplasia, mild atypia, moderate atypia, servere atypia or carcinoma. The classification accuracy of the procedure was more than 99% on trained data and was accomplished by minimizing the overlapping areas between the adjacent multivariate distributions of cell groups for selected features whose group means represent a monotonic function and for which the cell categories are distinguishable. The calculated ASI may reflect abnormal changes in the cell that may not be clearly evident visually. It appears that progression or reversal of bronchial epithelial atypia can be accurately monitored by studying the changes in the ASI, not only for preneoplasia but also for reactions to chemotherapy and various pulmonary infectious disease processes, such as influenza.

A mathematical and experimental simulation of the hematological response to weightlessness

Two ground-based methods of weightlessness simulation--a computer model of erythropoiesis feedback regulation and bedrest--were used to investigate the mechanisms which lead to loss of red cell mass during spaceflight. Both methods were used to simulate the first Skylab mission of 28 days. Human bedrest subjects lose red cell mass linearly with time and in this study the loss was 6.7% at the end of four weeks (compared to 14% in Skylab). Postbedrest recovery of red cell mass was delayed for two weeks during which time a further decline in this quantity was noted. This is consistent with the first Skylab mission but not with the two longer flights of two and three months. Hemoconcentration, observed early in the study, was essentially maintained despite red cell loss because of continued loss of plasma volume. The computer model, using the time-varying hematocrit data to estimate red cell production rates, predicted dynamic behavior of plasma volume and red cell mass that was in close agreement with the measured values. The results support the hypothesis that red cell loss during supine bedrest is a normal physiological feedback process in response to hemoconcentration enhanced tissue oxygenation and suppression of red cell production. In contrast, the delayed postbedrest recovery of red cell mass was more difficult to explain, especially in the light of enhanced reticulocyte indices observed at the onset on ambulation. Model simulation suggested the possibilities, still to be experimentally demonstrated, that this period was marked by some combination of increased oxygen-hemoglobin affinity, small reductions in mean red cell life span, ineffective erythropoiesis, or abnormal reticulocytosis. The question of whether hemoconcentration is the sole contributor to spaceflight red cell losses also remains to be resolved.

The lymphocyte response to influenza in humans

Enumeration of total lymphocytes and T, B, and null lymphocyte subpopulations in peripheral blood of normal volunteers was performed before and at intervals after inoculation with type A influenza virus. Volunteers who subsequently developed infection and illness had larger T-cell counts before inoculation and exhibited an increased number of B lymphocytes during the incubation period and a decrease in all subpopulations during illness, although the greatest decrease occurred in T cells. A decrease in B-cell counts occurred on day 3 in volunteers who exhibited infection, but no illness and no changes occurred in uninfected, well volunteers. Values had returned to baseline by day 21 after inoculation. Thus, the lymphopenia that accompanies influenza involves all subpopulations, but is primarily a decrease in T cells; in addition, differences in T-cell and B-cell populations before and during the incubation period may identify persons who will subsequently develop febrile influenza.

Response of the rat erythrocyte to ozone exposure

Sprague-Dawley rats were exposed to high (6--8 ppm) and moderate (1.5 ppm) amounts of ozone (O3) for various time periods. Response of the rat erythrocyte to ozone was monitored with red blood cell potassium (rubidium) influx studies, with storage stress combined with ultrastructural studies and with levels of erythrocyte glutathione peroxidase and superoxide dismutase. Erythrocytes of rats exposed to O3 showed no significant changes either in their potassium influx or in their glutathione peroxidase and superoxide dismutase activities compared to controls. Erythrocyte differential counts on O3-exposed animals showed significant changes initially as well as following storage stress compared to controls. Rats exposed to 8 ppm O3 for 4 h showed a marked increase in echinocytes. These consistent transformations from discocytes to echinocytes following O3 exposure suggest latent erythrocyte damage has occurred.

Response of the iron-deficient erythrocyte in the rat to hyperoxia

Normal and iron-deficient rats were exposed to 90% O2 at 760 Torr for 24 or 48 h. Erythrocyte response to hyperoxia was monitored by potassium (rubidium) influx studies, by storage stress, and by ultrastructural studies. Normal rat erythrocytes exhibited morphological changes and decrease of ouabain-sensitive potassium influx compared to unexposed controls. Both components of erythrocyte potassium influx were affected by iron deficiency. Erythrocytes from unexposed iron-deficient rats showed a 50% increase in ouabain-sensitive potassium influx compared to controls. Iron-deficient rats exposed to hyperoxia for 24 or 48 h, had erythrocytes with morphological changes. Erythrocytes of iron-deficient rats exposed for 24 h showed no influx change; those exposed for 48 h showed a decrease of ouabain-sensitive influx compared to erythrocytes of controls.

Sequential changes in body composition during infection: electron probe study IV

Alterations occur in human muscle electrolyte and water composition in response to infection. There appear to be at least two basic mechanisms; the first is an exchange of sodium for potassium without alteration in water content of muscle. The second is an increase in cellular Na and water without a loss of K on a dry weight basis. In a series of studies in monkeys, Salmonella typhimurium sepsis was induced as an experimental model. Both patterns of muscle response to infection were detected. Electron probe microanalysis revealed that the loss of K concentration was due to an accumulation of intracellular saline which dilute the K content. The mechanism of this is unclear; however, a concomitant increase in undertermined osmoles in the serum suggests that there may be an increase in organic osmoles within the cell which leads to the dilution of intracellular K concentration.

Cytofluorograf detection of Plasmodium yoelii, Trypanosoma gambiense, and Trypanosoma equiperdum by laser excited fluorescence of stained rodent blood

Samples of rat blood infected with Plasmodium yoelii (3% parasitized erythrocytes), Trypanosoma gambiense, or Trypanosoma equiperdum (greater than 50 trypanosomes per microscope field at 400 X) were fixed with 0.5% glutaraldehyde in phosphate buffered saline, then stained with acridine orange (AO) at 10(-4), 10(-5), or 10(-6) M for 0 to 15 min at 5 C or 25 C and/or ethidium bromide (EB) at 0.05 mg/ml for 20 min at 25 C. Stained cells were analyzed with a laser Cytofluorograf (Bio/Physics Systems, Inc.) to determine if parasites could be detected and differentiated from blood cells by their fluorescent characteristics. Samples of uninfected rat blood with and without leukocytes and P. yoelii-infected blood without leukocytes were treated similarly. In addition, suspensions of T. gambiense and T. equiperdum without all blood cells were stained with AO or EB and analyzed with the Cytofluorograf, as were mixed suspensions of both trypanosome species. EB- but not AO-stained P. yoelii-infected erythrocytes had fluorescent characteristics different from most blood cells. Neither AO- nor EB-stained T. gambiense or T. equiperdum could be differentiated from host blood cells or from each other. The results are discussed with respect to the use of laser flow systems in the detection and analysis of bloodstream dwelling protozoan parasites.

Hematology and immunology studies: the second manned Skylab mission

The hematologic and immunologic functions of the Skylab 3 (second manned mission) astronauts were examined during the preflight, inflight, and postflight phases of the 59-d mission in order to evaluate the response to and/or the influence of the space flight environment. Most changes observed were subtle and did not represent a threat to the health and safety of the crewmen during orbital flight. Even the most significant change observed, a reduction in the circulating red cell mass, did not have a detrimental influence on the astronaut cardiovascular or exercise responses as evaluated by other experiment protocols. Considering the facts that the data were not collected under ideally controlled conditions and that the astronauts were in excellent physical condition, the results of these studies would seem to indicate that man can function quite well in the space flight environment of the Skylab orbiting workshop for extended periods of time.

Fine structure of lymphocytes from an immune deficient child before and after administration of transfer factor

Lymphocytes from a male infant delivered by Cesarean section and placed into a germ-free environment were examined by electron microscopy (EM). The child had a sex-linked severe combined immunodeficiency. The lymphocytes were atypical, having sparse cytoplasm with little rough endoplasmic reticulum (ER) but abundant smooth ER. The nuclear membrane was pulled away from the nuclear space, and no evidence of nuclear pores or aggregated ribosomes was found. Mitochondria were intact. Repeated injections of the subject during the 9-month period with KLH, typhoid vaccine, and diphtheria toxoid yielded no significant observable change in the fine structure of the lymphocytes. At 11 months, the subject was given transfer factor. Following repeated injections of this material, the original cell type was still present but a new type of lymphocyte was also observed by EM examination. The new cell type resembled a more normal lymphocyte. It had a higher density of cytoplasmic material, in comparison with cells prior to administration of transfer factor. It was smaller in size with some aggregated ribosomes, had detectable amounts of rough ER, and more intact nuclear membranes. This new type of lymphocyte may represent a small population of B lymphocytes perhaps stimulated by T cells made immunocompetent by transfer factor.

Improved measurement of erythrocyte volume distribution by aperture-counter signal analysis

In aperture counters, particles in fluid suspension flow through a small orifice or aperture, causing a change in the electrical resistance of the aperture. This change is sensed by an external electronic circuit and translated into a voltage pulse, the signal height of which is proportional to the volume of the particle in the aperture. These signal pulses are collated into a spectrum of pulse heights by a multichannel pulse-height analyzer. The channel number (voltage increment) spectrum is proportional to the volume distribution of the particles sensed. A problem is that pulse height not only depends on cell volume, but also on the orientation and shape of the particle sensed and the current density along the path taken by the particle through the aperture. Uneven current density exists, primarily at the aperture entrance and exit, close to the wall. Orientation and shape of particles are altered near the wall by the unbalanced shear forces there. Toward the center of the aperture, the shear forces act so as not to induce continuous change in the orientation of the particles sensed. Thus introduction into the pulse-height spectrum of pulses that do not show a good proportionality to volume is primarily caused by particles that are traveling near the aperture wall. Residence time in the aperture for a particle traveling near the wall will be longer than that for a particle traveling down the center of the aperture, because of the smaller fluid velocity near the wall. Duration of the signal pulse created by a particle traveling near the wall will be correspondingly greater. We discuss an electronic filter to remove from the pulse-height spectrum those pulses that appear to result from particles traveling near the wall and the effect of the filter on the measured signal height and hence the volume distribution of erythrocytes. Use of this technique to characterize erythrocytes by volume distribution is described.

Postmission plasma volume and red-cell mass changes in the crews of the first two Skylab missions

Red-cell mass determinations were performed before and after the first two Skylab missions. The data showed a 14% mean decrease in red-cell mass after the 28-day mission and a 12% mean decrease after the 59-day mission. The red-cell mass returned to premission levels more slowly after the shorter (28-day) than after the longer mission. Plasma volume decreases were found after each mission. with the crew from the longer mission showing the greater change (13% vs. 8.4%). Postmission decreases in red-cell mass and plasma volume have been a general finding in crewmen who return from short or long spaceflight.

A paraprotein in severe combined immunodefeciency disease detected by immunoelectrophoretic analysis of plasma

A qualitative study was made of the plasma immunoglobulins of a child with severe combined immunodeficiency. By immunoelectrophoresis an immunoglobulin with an abnormal electrophoretic mobility was detected. This protein possessed mu heavy chain determinants, gave no detectable reaction with antisera specific for light chains, was of a relatively small molecular size, and was probably not composed of subunits held together by easily reduced disulfide bonds. The light chains that were present in this patient's plasma had a homogeneous electrophoretic mobility. The patient's plasma also contained at least two other immunoglobulins whose antigenic identity could not be established. One of these was abnormal in its electrophoretic mobility. The presence of the abnormal protein with mu determinants in the plasma of the second unrelated child with a similar disease suggests that the detection of this protein may have implications for the diagnosis or classification of immunodeficiency diseases.

Skylab experiment results: hematology studies

These studies were designed and coordinated to evaluate specific aspects of man's immunologic and hematologic systems which might be altered by or respond to the space flight environment. The biochemical functions investigated included cytogenetic damage to blood cells, immune resistance to disease, regulation of plasma and red cell volumes, metabolic processes of the red blood cell, and physical chemical aspects of red blood cell functions. Only minor changes were observed in the functional capacity of erythrocytes as determined by measuring the concentrations of selected intracellular enzymes and metabolites. Tests of red cell osmotic regulation indicated some elevation in the activity of the metabolic dependent Na-K pump, with no significant alterations in the cellular Na and K concentrations or osmotic fragility. A transient shift in red cell specific-gravity profile was observed on recovery, possibly related to changes in cellular water content. Measurements of hemoconcentration (hematocrit, hemoglobin concentration, red cell count) indicated significant fluctuations postflight, reflecting observed changes in red cell mass and plasma volume. There was no apparent reticulocytosis during the 18 days following the first manned Skylab mission in spite of a significant loss in red cell mass. However, the reticulocyte count and index did increase significantly 5 to 7 days after completion of the second, longer duration, flight. There were no significant changes in either the while blood cell count or differential. However, the capacity of lymphocytes to respond to an in vitro mitogenic challenge was repressed postflight, and appeared to be related to mission duration. The cause of this repression is unknown at this time. Only minor differences were observed in plasma protein patterns. In the second mission there were changes in the proteins involved in the coagulation process which suggested a hypercoagulative condition.

Resistance of erythrocytes of hibernating mammals to loss of potassium during hibernation and during cold storage

In two species of hibernators, hamsters and ground squirrels, erythrocytes were collected by heart puncture and the K content of the cells of hibernating individuals was compared with that of awake individuals. The K concentration of hamsters did not decline significantly during each bout of hibernation (maximum period of 5 days) but in long-term bouts in ground squirrels (i.e. more than 5 days) the K concentration of cells dropped significantly. When ground squirrels were allowed to rewarm the K content of cells rose toward normal values within a few hours. Erythrocytes of both hamsters and ground squirrels lose K more slowly than those of guinea pigs (nonhibernators) when stored in vitro for up to 10 days at 5 degrees C. In ground squirrels the rate of loss of K during storage is the same as in vivo during hibernation, and stored cells taken from hibernating ground squirrels also lose K at the same rate. The rate of loss of K from guinea pig cells corresponded with that predicted from passive diffusion unopposed by transport. The actual rate of loss of K from ground squirrel cells was slower than such a predicted rate but corresponded with it when glucose was omitted from the storage medium or ouabain was added to it. Despite the slight loss of K that may occur in hibernation, therefore, the cells of hibernators are more cold adapted than those of a nonhibernating mammal, and this adaptation depends in part upon active transport.

Temperature adaptation of active sodium-potassium transport and of passive permeability in erythrocytes of ground squirrels

Unidirectional active and passive fluxes of (42)K and (24)Na were measured in red blood cells of ground squirrels (hibernators) and guinea pigs (nonhibernators). As temperature is lowered, "active" (ouabain-sensitive) K influx and Na efflux were more greatly diminished in guinea pig cells than in those of ground squirrels. The fraction of total K influx which is ouabain sensitive in red blood cells of ground squirrels was virtually constant at all temperatures, whereas it decreased abruptly in guinea pig cells as temperature was lowered. All the passive fluxes (i.e., Na influx, K efflux, and ouabain-insensitive K influx and Na efflux) decreased logarithmically with decrease in temperature in both species, but in ground squirrels the temperature dependence (Q(10) 2.5-3.0) was greater than in guinea pig (Q(10) 1.6-1.9). Thus, red blood cells of ground squirrel are able to resist loss of K and gain of Na at low temperature both because of relatively greater Na-K transport (than in cells of nonhibernators) and because of reduced passive leakage of ions.