Immunomodulation by Histoplasma capsulatum products; polyclonal activation and mitogenic effects

The presence of reactive spleen cells to sheep red blood cells (SRBC) in nonimmunized BALB/c mice injected with histoplasmin, the culture filtrate of Histoplasma capsulatum, was monitored for 21 days following inoculation. Polyclonal activation, as evidenced by a sharp increase in the number of anti-SRBC rosetteforming cells (RFC), as well as an enhanced response to heterologous non-cross-reactive erythrocytes from other species, was found in the spleens of these rodents on Days 11 to 13. Elimination of B-cell-derived RFC by the addition of complement indicated that the erythrocyte-binding cells consisted of both T- and B-lymphocytes. An immunosuppressive effect was detected if histoplasmin was injected 2 days before the antigen (SRBC), but could be reversed by injecting the filtrate 30 min prior to the antigen, as is found with polyclonal activators displaying immunosuppressive activity. Histoplasmin also had a mitogenic effect on lymphocyte obtained from the spleen, bone marrow, and thymus similar in magnitude to that produced by lipopolysaccharide (LPS) and concanaval in A. The biological significance of these findings is discussed.     

Regulation of 3 beta-hydroxysteroid dehydrogenase activity by human chorionic gonadotropin, androgens, and anti-androgens in cultured testicular cells

delta 5-3 beta-Hydroxysteroid dehydrogenase is a key enzyme for testicular androgen biosynthesis and a marker for the Leydig cells. The hormonal regulation of this enzyme was studied in cultured rat testicular cells. Human chorionic gonadotropin (hCG) increased testosterone production in vitro while time course studies indicated a biphasic action of the gonadotropin on 3 beta-hydroxysteroid dehydrogenase activity. An initial stimulation (51%) of the enzyme was detected between 3 and 12 h of culture when medium testosterone was low. This is followed by an inhibition of 3 beta-hydroxysteroid dehydrogenase activity on days 2 and 3 of culture when medium testosterone was elevated. Concomitant treatment with a synthetic androgen (R1881) inhibited 3 beta-hydroxysteroid dehydrogenase activity and testosterone production in hCG-treated cultures while an anti-androgen (cyproterone acetate) increased 3 beta-hydroxysteroid dehydrogenase activity and testosterone biosynthesis. Addition of 10(-5) M spironolactone, an inhibitor of 17 alpha-hydroxylase, blocked the hCG stimulation of testosterone production but increased medium progesterone. In the absence of the secreted androgen, hCG stimulated 3 beta-hydroxysteroid dehydrogenase activity in a time- and dose-related manner. Furthermore, hCG stimulation of 3 beta-hydroxysteroid dehydrogenase activity and progesterone accumulation in spironolactone-supplemented cultures was decreased by concomitant treatment with R1881 but was not affected by cyproterone acetate. The inhibitory effect of R1881 was blocked by the anti-androgen. In the absence of hCG, treatment with testosterone, dihydrotestosterone, or R1881, but not promegestone, alone also inhibited 3 beta-hydroxysteroid dehydrogenase activity while the inhibitory effect of testosterone was blocked by cyproterone acetate. Thus, hCG stimulates 3 beta-hydroxysteroid dehydrogenase activity in cultured testicular cells. The androgenic steroidogenic end products, in turn, inhibit this enzyme. The hormonal regulation of 3 beta-hydroxysteroid dehydrogenase activity may be important in the ultrashort loop autoregulation of androgen biosynthesis.     

Immunosuppressive effect of Entamoeba histolytica extract on hamsters

The immune response to sheep red blood cells (SRBC) in mice and hamsters injected with an extract of entamoeba histolytica was studied. Both the primary and secondary immune response, measured by anti-SRBC antibody titers, were unaltered in the mouse, while a significant depression of the primary, but not the secondary, response was observed in the hamster. The effect was greatest when the amebic extract (AE) and SRBC were injected on the same day. The number of anti-SRBC rosettes formed in the spleen cells of hamsters treated with both AE and SRBC on day 0 was measured from days 1-16. The response peaked on day 13, while cells from animals injected with SRBC alone gave a maximal response on day 5. The formation of anti-SRBC rosettes in T-lymphocyte-enriched spleen cells treated with anti-gamma globulin serum and complement was almost abolished for the duration of the experiment. It is suggested that the mechanism responsible for this immunosuppressive phenomenon could involve early interference in the afferent limb of the immune response.     

Hydrolysis of bis(5''-nucleosidyl) polyphosphates by Escherichia coli 5''-nucleotidase.

Two enzymatic activities that split diadenosine triphosphate have been reported in Escherichia coli: a specific Mg-dependent bis(5'-adenosyl) triphosphatase (EC 3.6.1.29) and the bis(5'-adenosyl) tetraphosphatase (EC 3.6.1.41). In addition to the activities of these two enzymes, a different enzyme activity that hydrolyzes dinucleoside polyphosphates is described. After purification and study of its molecular and kinetic properties, we concluded that it corresponded to the 5'-nucleotidase (EC 3.1.3.5) that has been described in E. coli. The enzyme was purified from sonic extracts and osmotic shock fluid. From sonic extracts, two isoforms were isolated by chromatography on ion-exchange Mono Q columns; they had a molecular mass of about 100 kilodaltons (kDa). From the osmotic shock fluid, a unique form of 52 kDa was recovered. Mild heating transformed the 100-kDa isoform to a 52-kDa form, with an increase in activity of about threefold. The existence of a 5'-nucleotidase inhibitor described previously, which associates with the enzyme and is not liberated in the osmotic shock fluid, may have been responsible for these results. The kinetic properties and substrate specificities of both forms (52 and 100 kDa) were almost identical. The enzyme, which is known to hydrolyze AMP and uridine-(5')-diphospho-(1)-alpha-D-glucose, but not adenosine-(5')-diphospho-(1)-alpha-D-glucose, was also able to split adenosine-(5')-diphospho-(5)-beta-D-ribose, ribose-5-phosphate, and dinucleoside polyphosphates [diadenosine 5',5'-P1,P2-diphosphate,diadenosine 5',5'-P1,P3-triphosphate, diadenosine 5',5'-P1,P4-tetraphosphate, and bis(5'-guanosyl) triphosphate]. The effects of divalent cations and pH on the rate of the reaction with different substrates were studied.     

Centrally administered neuropeptide Y enhances the hypothermia induced by peripheral administration of adrenoceptor antagonists

The distribution of neuropeptide Y in the brain includes extensive coexistence within adrenaline- and noradrenaline-containing neurons and many of its actions are often associated with adrenergic systems. Since neuropeptide Y immunoreactivity is particularly intense in the preoptic area, one of the principal sites for thermoregulation, we have tested the effects of neuropeptide Y on core temperature in normothermic rats, and rats rendered hypothermic by systemic treatment with adrenergic antagonists. In the normothermic rat, intracerebroventricular administration of 1 microgram of neuropeptide Y did not have a significant effect on core temperature. Intraperitoneal treatment with the alpha 1-adrenoceptor antagonist, prazosin, or the beta-adrenoceptor antagonist, propranolol, caused an immediate and significant hypothermia; the intracerebroventricular administration of 1 microgram of neuropeptide Y, 10 minutes after these drugs, strongly potentiated their hypothermic effect. Although intraperitoneal treatment with the alpha 2-adrenoceptor antagonist, idazoxan, had no hypothermic effect per se, the intracerebroventricular administration of NPY 10 minutes after this antagonist led to a significant decrease in core temperature.     

Renal Cortical Basolateral Na+/HCO− 3 Cotransporter: IV Characterization and Localization with Polyclonal Antibodies

We have previously partially purified the basolateral Na⁺/HCO⁻ ₃ cotransporter from rabbit renal cortex and this resulted in a 400-fold purification, and an SDS-PAGE analysis showed an enhancement of a protein band with a MW of approximately 56 kDa. We developed polyclonal antibodies against the Na⁺/HCO⁻ ₃ cotransporter by immunizing Dutch-belted rabbits with a partially purified protein fraction enriched in cotransporter activity. Western blot analysis of renal cortical basolateral membranes and of solubilized basolateral membrane proteins showed that the antibodies recognized a protein with a MW of approximately 56 kDa. The specificity of the purified antibodies against the Na⁺/HCO⁻ ₃ cotransporter was tested by immunoprecipitation. Solubilized basolateral membrane proteins enriched in Na⁺/HCO⁻ ₃ cotransporter activity were incubated with the purified antibody or with the preimmune IgG and then reconstituted in proteoliposomes. The purified antibody fraction caused a concentration-dependent inhibition of the Na⁺/HCO⁻ ₃ cotransporter activity, while the preimmune IgG failed to elicit any change. The inhibitory effect of the antibody was of the same magnitude whether it was added prior to (inside) or after (outside) reconstitution in proteoliposomes. In the presence of the substrates (NaHCO₃ or Na₂CO₃) for the cotransporter, the inhibitory effect of the antibody on cotransporter activity was significantly blunted as compared with the inhibition observed in the absence of substrates. Western blot analysis of rabbit kidneys showed that the antibodies recognized strongly a 56 kDa protein band in microsomes of the inner stripe of outer medulla and inner medulla, but not in the outer stripe of outer medulla. A 56 kDa protein band was recognized in microsomes of the stomach, liver, esophagus, and small intestine but was not detected in red blood cell membranes. Localization of the Na⁺/HCO⁻ ₃ cotransporter protein by immunogold technique revealed specific labeling of the cotransporter on the basolateral membranes of the proximal tubules, but not in the brush border membranes. These results demonstrate that the polyclonal antibodies against the 56 kDa basolateral protein inhibit the activity of the Na⁺/HCO⁻ ₃ cotransporter suggesting that the 56 kDa protein represents the cotransporter or a component thereof. These antibodies interact at or near the substrate binding sites. The Na⁺/HCO cotransporter protein is expressed in different regions of the kidneys and in other tissues. Received: 27 January 1996/Revised: 23 July 1996     

Effect of CRF injected into the median eminence on GH secretion in female rats under different steroid status

To evaluate whether the median eminence (ME) is a site of action of CRF (corticotropin releasing factor) on GH secretion and to determine the possible role of estradiol and progesterone in modifying theses secretion, we injected CRF (0.25, 0.75, 1, and 1.5 nmol of peptide dissolved in 1 μl of water) directly into the ME in three experimental groups of rats: Long-term ovariectomized (OVX); OVX primed by estradiol (OVX±E) and OVX primed by estradiol plus progesterone (OVX±EP). Blood was collected to determine GH (30, 60, 90, and 120 min postinjection) Serum T₃, T₄, and glucose levels were measured in OVX±E rats 30 min postinjection. CRF at all doses studied significantly decreased serum GH levels in the three experimental groups. Serum T₃, T₄, and glucose levels were unchanged after CRF administration. The results suggest that: CRF inhibits “per se” GH secretion, at least in part, by a central action in the ME. The inhibitory effect of CRF on GH is independent of the estrogen/progesterone status of the animal. CRF at ME levels may participate in a variety of stress-related responses, including growth inhibition, through GH suppression.