Early protein synthesis in activated human peripheral blood mononuclear cells.

Though B-cell division and Ig synthesis in response to pokeweed mitogen (PWM) require interaction with T-cells and monocytes, it is not clear which earlier events in B-cell activation share this requirement, and which are the result of direct interaction of mitogen with the B-cell. Having previously shown that the acceleration of lecithin synthesis in human B-cells at 16-20 hr requires both T-cells and monocytes, we now examine whether B-cells require similar interactions to increase their protein synthetic rate, another important activation event. At 21-24 hr of PWM stimulation, the stimulation index (SI) for incorporation of [35S]methionine into protein was 2.1 +/- 0.4 for unfractionated cells, 1.7 +/- 0.1 for B-cells, 2.5 +/- 0.1 for T-cells, and 3.4 +/- 0.5 for monocytes. Thus monocytes contributed substantially to early mitogen-induced protein synthesis by human peripheral blood mononuclear cells. When the monocyte/B-cell fraction (MB) and T-cell fraction (T) were mixed at various ratios in PWM-stimulated cultures, synergy was apparent at MB:T ratios of 1:1 and 1:2, indicating cell interactions augmented early mitogen-driven protein synthesis in at least one of these cell types. However, much or all of this synergy could be attributed to T-cells, whose protein synthetic response was augmented by B-cells and monocytes. In contrast, the early increase in B-cell protein synthesis appeared to be independent of cell interactions, since their SI of 1.7 was not influenced by varying the proportion of M- or T-cells over a 50-fold range. These contrasting results between two contemporary events fits the hypothesis that one (accelerated phospholipid synthesis) requires a first signal plus one or more cell interaction signals, whereas the other (accelerated protein synthesis) requires only the first signal.

Insulin-like growth factor-I binds selectively to human peripheral blood monocytes and B-lymphocytes.

Insulin-like growth factor-I (IGF-I) is a potential modulator of responses to a variety of immunological challenges. Previous studies have suggested that specific IGF-I receptors are present on peripheral blood leukocytes, including polymorphonuclear leukocytes, lymphocytes, and monocytes. We sought to determine what type of IGF receptor was present on peripheral blood mononuclear cells and which types of cells possessed these receptors. Binding of [125I]IGF-I to mononuclear cells was inhibited by both unlabeled IGF-I and insulin, insulin being 200-fold less potent than IGF-I. Covalent affinity labeling with [125I]IGF-I, followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography, revealed a specific binding species with an apparent mol wt of 130 kDa. Two color flow cytometric analysis of mononuclear cells stained with mouse monoclonal antibodies specific for the human IGF-I receptor, the human insulin receptor, and monoclonal antibodies directed against specific monocyte and lymphocyte subset cell surface antigens revealed that both IGF-I receptors and insulin receptors were present on nearly all monocytes and B-lymphocytes, but were present on only 2% of T-lymphocytes. We conclude from these data that among human peripheral blood nonactivated mononuclear cells, IGF-I binds to specific type I IGF receptors found predominantly on monocytes and B-lymphocytes.

The pathophysiology of acute high-altitude illness.

Complex physiologic responses occur as nonacclimatized lowland dwellers ascend above 10,000 feet, with a resulting partial pressure of arterial oxygen of less than 60 mm Hg. There are marked hemodynamic changes and shifts in body fluids that may result in organ dysfunction. The suspected pathogenesis of these acute hypobaric hypoxic-induced illnesses is discussed. Cerebral dysfunction may present as acute mountain sickness or high-altitude cerebral edema. Usually asymptomatic high-altitude retinal hemorrhage and noncardiogenic high-altitude pulmonary edema also are described. All of these illnesses apparently represent a spectrum of pathologic states initiated by an exaggerated vascular response to hypoxia. With the exception of retinopathy, high-altitude illness can be prevented by slow ascent. Early recognition of cerebral or pulmonary edema and immediate descent will prevent serious consequences of nonacclimatized persons who are acutely exposed to hypobaric environments.

Activation of T lymphocytes by 12-O-tetradecanoylphorbol-13-acetate is resistant to inhibition by cyclosporin A.

Cultured T lymphocytes from pig blood can be activated by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). Activation is additive with that induced by the mitogenic lectin phytohaemagglutinin (PHA). Activation by TPA differs from that induced by PHA or other mitogenic lectins in that it is not inhibited even by high concentrations of the immunosuppressive drug cyclosporin A (CS-A). Neither co-culture of lymphocytes with PHA and TPA nor addition of culture supernatants from TPA-stimulated cultures affected the sensitivity to CS-A of the response to PHA.

Cerebral blood velocity and other cardiovascular responses to 2 days of head-down tilt.

Spaceflight induces a cephalad redistribution of fluid volume and blood flow within the human body, and space motion sickness, which is a problem during the first few days of spaceflight, could be related to these changes in fluid status and in blood flow of the cerebrum and vestibular system. To evaluate possible changes in cerebral blood flow during simulated weightlessness, we measured blood velocity in the middle cerebral artery (MCA) along with retinal vascular diameters, intraocular pressure, impedance cardiography, and sphygmomanometry on nine men (26.2 +/- 6.6 yr) morning and evening for 2 days during continuous 10 degrees head-down tilt (HDT). When subjects went from seated to head-down bed rest, their heart rate and retinal diameters decreased, and intraocular pressures increased. After 48 h of HDT, blood flow velocity in the MCA was decreased and thoracic impedance was increased, indicating less fluid in the thorax. Percent changes in blood flow velocities in the MCA after 48 h of HDT were inversely correlated with percent changes in retinal vascular diameters. Blood flow velocities in the MCA were inversely correlated (intersubject) with arterial pressures and retinal vascular diameters. Heart rate, stroke volume, cardiac output, systolic arterial pressure, and at times pulse pressure and blood flow velocities in the MCA were greater in the evening. Total peripheral resistance was higher in the morning. Although cerebral blood velocity is reduced after subjects are head down for 2 days, the inverse relationship with retinal vessel diameters, which have control analogous to that of cerebral vessels, indicates cerebral blood flow is not reduced.

Intraocular pressure and retinal vascular changes during transient exposure to microgravity.

We measured intraocular pressures and retinal vascular diameters from 11 subjects during 20 seconds of microgravity produced by parabolic flight on board a KC-135 aircraft. Intraocular pressures increased 58% during parabolic flight compared to baseline values (19 +/- 1 mm Hg vs 12 +/- 1 mm Hg, respectively; P < .001). A 4% reduction in the caliber of retinal arteries was also noted during microgravity, but this change did not achieve statistical significance (7.8 +/- 0.3 pixels at zerogravity vs 8.1 +/- 0.3 pixels at 1g; P = .07). The increase in intraocular pressure and trend of arteries to constrict are thought to result from cephalad shifts in intravascular and extravascular body fluids as a result of the absence of the 1g hydrostatic gradient. The results of our study confirm that this fluid shift and its effects on the eye occur rapidly, within 20 seconds of exposure to microgravity.

Psychosocial correlates of immune responsiveness and illness episodes in US Air Force Academy cadets undergoing basic cadet training.

This study examined psychosocial correlates of immune function and illness in 89 male first-year US Air Force Academy cadets. A psychosocial questionnaire was administered to cadets prior to their arrival at the academy and was readministered during cadet orientation and during the stressful environment of Basic Cadet Training (BCT). Immune responsiveness was analyzed by PHA-, PMA-, or anti-CD3-stimulated thymidine uptake in mononuclear leucocytes. Illness episodes were assessed via medical chart review and self-reported symptoms. There were significant increases in distress levels as cadets entered BCT. No psychosocial measure assessed prior to arrival at the academy predicted level of PHA-, PMA-, and anti-CD3-stimulated thymidine uptake or risk of illness. However, hostility levels reported during BCT predicted risk of illness in the four weeks following psychosocial assessment (odds ratio = 7.1; 95% confidence interval: 1.4-36.1). Elevated response to environmental stressors and lower well-being levels also predicted impending illness, but only in the cohort of cadets who had not contracted food poisoning prior to assessment during BCT (OR = 9.3, CI = 1.9-46.7; OR = 0.09, CI = 0.02-0.53). These results suggest that self-report measures of hostility, response to environmental stressors and well-being may be useful predictors of impending illness episodes in males encountering high stress environments.

The effect of naproxen on acute mountain sickness and vascular responses to hypoxia.

The role of prostaglandins in the pathogenesis of acute mountain sickness and two hypoxia-induced vascular responses was evaluated using the cyclooxygenase inhibitor naproxen. Eleven men spent 24 hours at sea level, followed by 34 hours of decompression to 428 mm Hg while receiving naproxen (N), 250 mg twice daily or placebo (P) in a double-blind crossover trial. Serum naproxen levels measured by high pressure liquid chromatography were not changed by hypoxia. The severity of acute mountain sickness (AMS) by the Environmental Symptom Questionnaire scores and observer assessment were unaffected by drug treatment. Retinal artery diameter measured from projected fundus photographs was increased after 27 hours at altitude (11.4 +/- .5 mm) vs. sea level (9.4 +/- .5 mm, p less than 0.05) during both trials. Upright mean arterial pressure fell after 6 hours at altitude (79 +/- 3 mm Hg during N and P vs. 92 +/- 3 at sea level, p less than 0.01). Minute ventilation, end expiratory alveolar PO2 and PCO2 did not differ between drug trials. This study suggests vasodilating prostaglandins do not have a major role in the genesis of AMS, hypoxia-induced retinal vasodilatation, or postural blood pressure responses in man.

Renin, aldosterone, and vasopressin responses to hypoxia during 6 hours of mild exercise.

The effect of hypoxia (H) on plasma renin (PRA), aldosterone (PA), and arginine vasopressin levels (AVP) was evaluated during 6 h of mild exercise (treadmill: 0 grade, 1 mph). A crossover study was performed on seven male volunteers during steady state conditions of H2O, Na+ and K+ balance while breathing 12.5% O2 (PaO2 42 +/- 3 mm Hg) and room air (N, 21% O2). After exercise there were no significant differences in body weight, hematocrit, calculated plasma volumes, serum or urine osmolality, urine Na+ or K+ excretion or AVP. Mean arterial pressure (MAP) while exercising was reduced during hypoxia (86 +/- 2 vs. 92 +/- 4 mm Hg), p less than 0.05. Normal diurnal variation in serum cortisol was lost during exercise (N and H). Plasma renin and aldosterone levels fell with exercise in both groups: PRA N 3.3 to 2.4 vs. H 4.9 to 2.3 ng X ml-1 X h-1; PA N 6.5 to 2.8 vs. H 9.3 to 2.3 ng X dl-1 (p less than 0.05). Hypoxia per se did not exert influence beyond mild exercise regarding serum osmolality, urine osmolality or Na+ or K+ excretion. Sustained hypoxia during 6 h of mild exercise despite a lower MAP failed to elevate PRA, aldosterone, or AVP levels when normal hydration is maintained.

Immune responsiveness and risk of illness in U.S. Air Force Academy cadets during basic cadet training.

It has been proposed, but not confirmed, that environmental stressors alter immune function and increase the risk of viral infection among healthy individuals. We evaluated this hypothesis, examining the relationship among stress, immune function, and illness in 96 first-year U.S. Air Force Academy cadets during orientation and 4 weeks later during the stressful environment of Basic Cadet Training (BCT). Perceived stress and well-being levels of cadets were assessed via questionnaire. Immune responsiveness was analyzed by PHA-stimulated thymidine uptake in mononuclear leucocytes and by serologic evidence of reactivation of the Epstein-Barr virus (EBV). We documented significant declines in in vitro PHA-induced lymphocyte transformation (-35%; p less than 0.05) and subjective well-being (-19%; p less than 0.05) from orientation to BCT with corresponding, significant increases in perceived stress (+32%; p less than 0.05). Despite significantly altered in vitro immune responsiveness, there was no serologic evidence of EBV reactivation nor was there an association between these measures and risk of illness as determined by medical chart review and self-reported symptoms. These results suggest that reduced in vitro immune responsiveness during a moderate stressor may not necessarily lead to an increased risk of infection and/or reactivation of EBV in normal individuals.

Intraocular pressure, retinal vascular, and visual acuity changes during 48 hours of 10 degrees head-down tilt.

Intraocular pressures, retinal vascular diameters, and visual acuities of nine men (ages 19-29), were repeatedly measured while the subjects were tilted 10 degrees head-down for 48 h and while they were seated before (baseline), and after the tilt. An immediate increase in intraocular pressure, measured by pneumatonometer (4.7 +/- 0.6 mm Hg, p less than 0.001) was recorded when subjects assumed the head-down position, and diurnal variations in intraocular pressures were observed for the 48 h. The initial and final head-down intraocular pressures were not significantly different (18.9 +/- 1.2 mm Hg vs. 17.9 +/- 1.4 mm Hg, respectively). However, when subjects resumed the sitting position, intraocular pressures fell below the initial sitting values (14.2 +/- 0.9 pre vs. 11.2 +/- 0.5 post, p less than 0.04). Computer image analysis of the retinal vasculature detected a 6% and 2% reduction in the caliber of arteries and veins, respectively, as compared with sitting baseline values. No changes in visual acuity were documented during the 48 h of head-down tilt. Our data suggest that the choroidal blood reservoir increases in volume over 48 h at continuous head-down position with a compensatory decrease in aqueous volume. These findings may explain intraocular pressure changes noted in astronauts during previous space missions and in studies associated with change in body position.

Dexamethasone for prevention and treatment of acute mountain sickness.

We wished to determine in a field study the effectiveness of dexamethasone for prevention and treatment of acute mountain sickness (AMS). Prevention Trial: We transported 15 subjects from sea level to 4,400 m (PB = 400 mm Hg) on Denali (Mt. McKinley) by means of a 1-h helicopter flight. In a randomized, double-blind fashion we gave eight subjects a placebo and seven subjects 2 mg dexamethasone orally every 6 h, starting 1 h before take-off. The entire placebo group and five of the dexamethasone group developed AMS within 5 h, and became progressively more ill until 12 h when the trial was terminated. We concluded that 2 mg of dexamethasone every 6 h did not prevent AMS in active soldiers rapidly transported to high altitude. Treatment Trial: We treated 11 of those with moderate to severe AMS (symptom score 4.5 +/- 0.7, range 3 to 11) with 4 mg of dexamethasone every 6 h orally or intramuscularly for 24 h. All were markedly improved at 12 h (symptom score 1.0 +/- 0.3, p less than 0.001, range 0 to 3), but symptoms increased after the drug was discontinued at 24 h (symptom score = 2.4 +/- 0.5). We conclude that dexamethasone in a dosage of 4 mg PO or IM every 6 h is an effective treatment for AMS, but that illness may recur with abrupt discontinuation of the drug.

Immune suppression at high altitude.

This paper is a review and interpretation of prior studies that have investigated the effects of hypoxia on immune function. A summary of current methods used to assess immune effector cell function in human beings is presented using in vitro models of mononuclear cell activation. Animal studies indicate that impaired host defenses against bacterial pathogens may be compromised, but that resistance to virus infections may remain intact. Data from human studies and animal models indicate that active immunization and B cell function are unimpaired, whereas T cell function is blunted following exposure to hypoxia. Mechanisms that may be responsible for alterations in normal immunoregulation are presented. The implications of altered immune function in subjects exposed to high altitude are discussed.

Pregnancy among patients with systemic lupus erythematosus receiving immunosuppressive therapy.

We evaluated retrospectively the effect of superimposed pregnancy upon the course of systemic lupus erythematosus (SLE) in patients receiving glucocorticoids or azathioprine at conception. About equal numbers of flares (10 vs 12) occurred among 22 pregnant patients with lupus and 22 nonpregnant control patients with lupus matched by disease duration and prior organ system involvement. Pregnancy per se did not appear to accelerate SLE in patients receiving immunosuppressive therapy.

Pregnancy in patients with systemic lupus erythematosus.

This retrospective study of 31 patients with systemic lupus erythematosus during 38 pregnancies shows a spontaneous or missed abortion rate of 7.9%, elective abortion rate of 10.5%, and a perinatal mortality rate of 12.9%. There was one maternal death 5 weeks post partum. If the onset of systemic lupus erythematosus during pregnancy included nephritis or significant thrombocytopenia, the mothers were acutely ill. All of the perinatal mortality occurred in these patients. Management of systemic lupus erythematosus during pregnancy need not differ from that in the nonpregnant state. However, immunosuppressive therapy should not be diminished or discontinued during pregnancy. Clinical parameters, renal function studies, and hematologic information were far more useful than immunologic laboratory data in assessing the course of systemic lupus erythematosus during pregnancy and indicating alterations in treatment. Antepartum fetal surveillance is advised. The timing of and route of delivery must be individualized, and systemic lupus erythematosus in and of itself is not an indication for delivery by cesarean section.

An automated method of quantifying retinal vascular responses during exposure to novel environmental conditions.

The width of retinal arteries and veins was measured by digital image analysis using an automated vessel-tracking software program. Mean coefficients of variations in vessel width of less than 3% were easily achieved from digitized 35-mm retinal photographs taken with a table-top or hand-held fundus camera. Retinal images were analyzed from seven subjects exposed to sea level or altitudes equivalent to 10,000 (3048 m), 17,500 (5334 m), and 25,000 (7620 m) ft and nine subjects exposed to sea level and 14,110 ft (4300 m). At each altitude, retinal veins dilated more than did arteries (5 +/- 1 versus 0 +/- 1% at 10,000 ft and 28 +/- 9% versus 9 +/- 2% at 25,000 ft; veins versus arteries, respectively). However, widths of retinal arteries and veins were reduced in nine subjects tested after 15 minutes, 24 hours, and 48 hours of 10 degrees head-down tilt; and values varied inversely with intraocular pressures (IOP). Hand-held retinal fundus photography and digital image analysis were found to provide a sensitive and objective method for detecting and quantifying retinal vascular responses in humans exposed to novel environments.

Alteration in human mononuclear leucocytes following space flight.

Reduced in vitro mitogen-stimulated proliferative responses have routinely been observed from astronauts' mononuclear leucocytes following space flight. This study investigated the effect of space flight on subpopulations of peripheral blood mononuclear cells from 30 shuttle astronauts prior to launch, upon landing and 3 days after flight. The total number of peripheral blood leucocytes, granulocytes and monocytes were increased after space flight (5.7 +/- 0.2 versus 7.0 +/- 0.2; 3.1 +/- 0.1 versus 5.0 +/- 0.1; and 0.16 +/- 0.02 versus 0.25 +/- 0.28 x 10(3) cells/mm3, respectively) whereas lymphocytes were decreased (2.2 +/- 0.1 versus 1.7 +/- 0.1 x 10(3) cells/mm3). Flow cytometry analysis on Ficoll-Hypaque isolated mononuclear cells upon landing revealed significant decreases in T-inducer (CD4+, Leu-8+; 32 +/- 2 versus 23 +/- 2%) and T-cytotoxic lymphocytes (CD8+, CD11b-; 17 +/- 1 versus 12 +/- 1%), and increases in monocytes (CD14+; 13 +/- 1 versus 21 +/- 1%) compared to pre-flight and post-flight samples whereas B cells (CD19+), T-helper (CD4+, Leu-8-) and T-suppressor (CD8+, CD11b+) populations did not change. Additional phenotypic analysis of these mononuclear leucocytes from 10 crew members upon landing revealed a reduction in natural killer (NK) cells (CD16+ or CD56+; 9 +/- 1 versus 3 +/- 1%) and an increase in monocytes that were negative for insulin and insulin-like growth factor-1 (IGF-1) receptor expression. Flow cytometric analysis indicated these hormone receptor negative monocytes were smaller and less granular than receptor positive monocytes. Therefore, a novel population of monocytes may be released into the peripheral blood during the stress of space flight or upon landing. These findings may explain some of the diverse in vitro immunological and endocrine changes observed in crew members following space flight.