The D-amino acid transport by the invertebrate SLC6 transporters KAAT1 and CAATCH1 from Manduca sexta

The ability of the SLC6 family members, the insect neutral amino acid cotransporter KAAT1(K⁺‐coupled amino acid transporter 1) and its homologous CAATCH1(cation anion activated amino acid transporter/channel), to transport D‐amino acids has been investigated through heterologous expression in Xenopus laevis oocytes and electrophysiological techniques. In the presence of D‐isomers of leucine, serine, and proline, the msKAAT1 generates inward, transport‐associated, currents with variable relative potencies, depending on the driving ion Na⁺ or K⁺. Higher concentrations of D‐leucine (≥1 mmol/L) give rise to an anomalous response that suggests the existence of a second binding site with inhibitory action on the transport process. msCAATCH1 is also able to transport the D‐amino acids tested, including D‐leucine, whereas L‐leucine acts as a blocker. A similar behavior is exhibited by the KAAT1 mutant S308T, confirming the relevance of the residue in this position in L‐leucine binding and the different interaction of D‐leucine with residues involved in transport mechanism. D‐leucine and D‐serine on various vertebrate orthologs B⁰AT1 (SLC6A19) elicited only a very small current and singular behavior was not observed, indicating that it is specific of the insect neutral amino acid transporters. These findings highlight the relevance of D‐amino acid absorption in the insect nutrition and metabolism and may provide new evidences in the molecular transport mechanism of SLC6 family.

Detection of red blood cell antibodies in mitogen-stimulated cultures from patients with hereditary spherocytosis

BACKGROUND

Hereditary spherocytosis (HS) is a congenital hemolytic anemia caused by defects in red blood cell (RBC) membrane proteins leading to premature RBC clearance in the spleen. The presence of RBC autoantibodies has never been extensively investigated in HS.

STUDY DESIGN AND METHODS

RBC antibody-bound immunoglobulin (Ig)G was investigated in 91 consecutive HS patients by mitogen-stimulated direct antiglobulin test (MS-DAT), a sensitive method able to magnify latent RBC antibody autoimmunity and related with hemolytic variables, previous splenectomy, and type of membrane defect.

RESULTS

A total of 61% of HS cases had RBC antibodies by MS-DAT (29 Band 3, 17 spectrin deficiency, and nine no defined defect). The amount of RBC-bound IgG was greater in HS compared with controls (236 ± 192 ng/mL vs. 52 ± 29 ng/mL, p < 0.0001), although lower than that observed in autoimmune hemolytic anemia (AIHA; 634 ± 371 ng/mL vs. 236 ± 192 ng/mL, p < 0.0001). Western blot experiments showed that purified IgG fraction from MS-DAT-positive patients bind to α- and β-spectrin, Band 3, and Band 4.9. Positive cases displayed increased reticulocytosis and slightly reduced hemoglobin (Hb) values compared to negative ones. Patients displaying RBC-bound IgG of more than 250 ng/mL (the positive threshold of AIHA) showed increased number of spherocytes and mainly had spectrin deficiency. RBC-bound IgG and free Hb increased over time after storage at 4°C, a surrogate of ex vivo aging, more evidently in HS than controls, and particularly in Band 3 deficiency.

CONCLUSION

RBC autoantibodies were detected by MS-DAT in more than a half of HS patients. Positive cases showed a more evident hemolytic pattern suggesting a pathogenic role of these autoantibodies in RBC opsonization and splenic removal.

Bone marrow mitogen-stimulated direct antiglobulin test in a case of erythroblastic synartesis

In this article we report a case of erythroblastic synartesis, a rare disease characterized by ineffective erythropoiesis, clusters of erythroblasts due to membrane invaginations, in which an autoimmune pathogenesis is hypothesized. We investigated the presence of anti-erythroblast autoimmunity in bone marrow cultures using a mitogen-stimulated direct antiglobulin test, a method reported to be able to disclose a latent autoimmunity in various diseases. The test revealed the presence of erythroblast-bound IgG, supporting the hypothesis of the autoimmune pathogenesis of erythroblastic synartesis. Supernatants induced the same specific morphological features, i.e erythroblastic clustering and diserythropoietic signs (multiple nuclei, nuclear inclusions, and intercellular bridges) in normal progenitors.

Anti-erythroblast autoimmunity in early myelodysplastic syndromes

BACKGROUND AND OBJECTIVES

Autoimmune phenomena, mainly directed against red blood cells are described in myelodysplastic syndromes (MDS), particularly early MDS, i.e. refractory anemia (RA) and RA with ringed sideroblasts (RARS). Dysregulation of apoptosis and immunoregulatory cytokines are thought to play a role in the pathogenesis of MDS.

DESIGN AND METHODS

This work was aimed to investigate anti-erythroid autoimmunity in unstimulated and mitogen-stimulated peripheral blood and bone marrow cultures of 26 patients with early MDS (RA and RARS), and to relate its presence with apoptotic markers and cytokine production. Bone marrow cytokine production in culture supernatants, and caspase-3 and nuclear factor-kappaB activity in cell extracts were tested by enzyme-linked immunosorbent assays.

RESULTS

Fourteen of the 26 (53.8%) patients showed the presence of autoantibodies in bone marrow cultures, whereas none displayed a positive direct antiglobulin test in peripheral blood cultures. Incubation of culture supernatants from positive patients with autologous CD45- enriched-cell suspensions showed that the autoimmune reaction was directed against autologous erythroblasts. These patients had mild signs of hemolysis and increased numbers of erythroblasts, compared with negative patients. Patients with anti-erythroblast autoimmunity displayed higher caspase-3 activity and lower tumor necrosis factor-alpha and interleukin-4 production than did negative patients.

INTERPRETATION AND CONCLUSIONS

Half of the patients with early MDS showed autoimmunity against erythroblasts. This evidence might support a more rationale use of steroid therapy in these patients. The lower levels of cytokines in patients with anti-erythroblast autoimmunity are consistent with the suggested hypothesis that the autoimmune phenomena observed in MDS are probably initiated and perpetuated through alterations of pro-inflammatory and/or immunoregulatory cytokine production.

In vitro production of anti-RBC antibodies and cytokines in chronic lymphocytic leukemia

B-chronic lymphocytic leukemia (B-CLL) patients have a high prevalence of autoimmune phenomena, mainly autoimmune hemolytic anemia (AIHA). Immunoregulatory cytokines play a role in the regulation of both autoimmunity and leukemic B-cell growth. Mitogen-stimulated direct antiglobulin test (MS-DAT) is a recently described test able to disclose latent anti-RBC autoimmunity in AIHA. We investigated the prevalence of anti-RBC autoimmunity by MS-DAT and the pattern of cytokine production by PHA-stimulated whole blood cultures from 69 B-CLL patients and 53 controls. Results showed that anti-RBC IgG values in unstimulated, PHA-, PMA-, and PWM-stimulated cultures were significantly higher in B-CLL patients compared with controls. In B-CLL, the prevalence of anti-RBC autoimmunity was 28.9% by MS-DAT, compared with 4.3% by the standard DAT. Production of IFN-gamma, IL-2, IL-13, TNF-alpha, sCD23, and sCD30 was significantly increased in all B-CLL patients compared with controls, whereas there was no difference in IL-4, IL-6, IL-10, and TGF-beta production. Multivariate analysis showed that IL-4 was significantly increased in MS-DAT-positive compared with -negative patients. Patients with autoantibody positivity displayed greater IFN-gamma production than negative patients. These data are in line with the hypothesis that autoimmune phenomena in B-CLL are associated with an imbalance towards a Th-2-like profile. The elevated prevalence of anti-RBC autoimmunity found by MS-DAT suggests that an underestimated latent autoimmunity exists in B-CLL.

Increased Mycobacterium tuberculosis growth in HIV-1-infected human macrophages: role of tumour necrosis factor-alpha

Synergism between Mycobacterium tuberculosis (M. tuberculosis) and HIV-1 infections was demonstrated in several in vitro models and clinical studies. Here, we investigated their reciprocal effects on growth in chronically HIV-1-infected promonocytic U1 cells and in acutely infected monocyte-derived macrophages (MDM). Phagocytosis of M. tuberculosis induced HIV-1 expression in U1 cells, together with increased TNF-alpha production. M. tuberculosis growth, evaluated by competitive PCR, was greater in HIV-1-infected MDM compared to uninfected cells. M. tuberculosis phagocytosis induced greater TNF-alpha and IL-10 production in HIV-1-infected MDM than in uninfected cells. In uninfected MDM, addition of TNF-alpha and IFN-gamma decreased, whereas IL-10 increased M. tuberculosis growth. On the contrary, in HIV-1-infected MDM, addition of TNF-alpha and IFN-gamma increased, whereas IL-10 has no effect on M. tuberculosis growth. TNF-alpha seems to play a pivotal role in the enhanced M. tuberculosis growth observed in HIV-1-infected MDM, being unable to exert its physiological antimycobacterial activity. Here, for the first time we demonstrated an enhanced M. tuberculosis growth in HIV-1-infected MDM, in line with the observed clinical synergism between the two infections.