Ambak Kumar Rai

Regulatory T cells suppress T cell activation at the pathologic site of human visceral leishmaniasis.

Suppression of T cell response is thought to be involved in the pathogenesis of visceral leishmaniasis (VL). Regulatory T cell (Treg) mediated immune-suppression is reported in animal models of Leishmania infection. However, their precise role among human patients still requires pathologic validation. The present study is aimed at understanding the frequency dynamics and function of Treg cells in the blood and bone marrow (BM) of VL patients. The study included 42 parasitologically confirmed patients, 17 healthy contact and 9 normal bone marrow specimens (NBM). We show i) the selective accumulation of Treg cells at one of the disease inflicted site(s), the BM, ii) their in vitro expansion in response to LD antigen and iii) persistence after successful chemotherapy. Results indicate that the Treg cells isolated from BM produces IL-10 and may inhibit T cell activation in IL-10 dependent manner. Moreover, we observed significantly higher levels of IL-10 among drug unresponsive patients, suggesting their critical role in suppression of immunity among VL patients. Our results suggest that IL-10 plays an important role in suppression of host immunity in human VL and possibly determines the efficacy of chemotherapy.

High concentration of adenosine in human visceral leishmaniasis despite increased ADA and decreased CD73

Absence of an effective Th‐1 response has been demonstrated as a major cause for the disease pathology among patients with visceral leishmaniasis (VL). Defining strategies to prevent the development of Th‐2 response and/or initiate/activate effective Th‐1 response may be of help to reduce the growing incidence of drug unresponsiveness. Adenosine, which is considered as an endogenous anti‐inflammatory agent is generated in injured/inflamed tissues by the enzymatic catabolism of adenosine triphosphate (ATP), and it suppresses inflammatory responses of essentially all immune cells. The extracellular adenosine‐producing pathway comprises two major enzymes CD39 (ATP→ADP→AMP) and CD73 (AMP→Adenosine). In contrast, the adenosine‐degrading pathway contains only one major enzyme adenosine deaminase (ADA). Our study shows high concentration of adenosine in diseased condition, varying expression of enzyme involved in adenosine‐producing (CD73↓) and adenosine‐degrading (ADA↑) pathways. These are less studied in infections like VL but are very important in terms of endogenous regulation of immune response among patients.

Early activated Th-1 type and dominantly diverse natural killer T (CD3⁺CD161⁺Vα24⁻) cells in bone marrow among visceral leishmaniasis patients.

Lipid antigens of Leishmania donovani-like lipophosphoglycans (LPG) are demonstrated to be a potent ligand for natural killer T (NKT) cell activation. Little is known about the phenotype or function of these cells and their trafficking pattern to the bone marrow (BM) of visceral leishmaniasis (VL) patients. Their precise role in humans still requires pathological validation. The study included 42 parasitologically confirmed patients (mean age 24.80±16.26 years; range 3-70 years; 25 males and 17 females), 33 healthy contact subjects (family/non-family members) and normal BM specimens (NBM; n=9). Enumeration of NKT cells and quantification of parasites (before and after therapy) were performed for the recruited patients. Results established that non-CD1d restricted, diverse cells are the dominant population among resident but not enriched NKT (CD3⁺CD161⁺) cells at the disease site (BM). Expression profiles for various markers are indicative of their early activated (CD69⁺, CD62L(low), CD11a(high)) CCR5⁺ phenotype at the BM. Functionally, BM-derived NKT cells were dominantly producing IFN-γ in response to L. donovani antigen in vitro. Given these observations, these data indicate that CD3⁺CD161⁺ diverse NKT cells are heterogeneous in function and of the dominant Th-1 phenotype at the disease site.

Induction of lepromin reactivity in cured lepromatous leprosy patients: impaired chemokine response dissociates protective immunity from delayed type hypersensitivity

Delayed Type Hypersensitivity (DTH) and protective immunity are thought to be tightly linked. Remarkable similarity exists between their cellular and immune mechanisms. However, their dissociation is also well known. Here we investigate the immunological mechanisms relevant for their dissociation in a group of non-relapsing cured lepromatous leprosy (CLL) patients. In these patients, using lepromin reaction as a model system of DTH we report critical role of tissue chemokine response in synchronous manifestation of these linked phenomena. Results indicate elevation of the threshold of tissue chemokine induction thus dissociating DTH from protective immunity in lepromin -ive CLL patients. We also show that the DTH anergy in these subjects is not an absolute one but depends on the strength of the stimulus. Our data provide insights into the intricate relationship between DTH and immunity and highlight the persistent presence of effector immune mechanisms involving these two pathways in apparently unresponsive lepromatous leprosy patients.

Enrichment of invariant natural killer T cells in the bone marrow of visceral leishmaniasis patients

Lipid antigens of Leishmania donovani like lipophosphoglycans are shown as a potent ligand for the activation of invariant natural killer T (iNKT) cells. It is reported that activation of iNKT cells augments the disease pathology in experimental visceral leishmaniasis (VL). In this study, we demonstrate the enrichment of iNKT cells in the bone marrow, one of the disease sites among patients with VL.

Expression of CD13/aminopeptidase N in precursor B-cell leukemia: role in growth regulation of B cells

Expression of cell surface CD13 in acute B-cell leukemia (ALL-B) is often viewed, as an aberrant expression of a myeloid lineage marker. Here, we attempted to study the stage specific expression of CD13 on ALL-B blasts and understand its role in leukemogenesis as pertaining to stage of B-cell ontogeny. A total of 355 cases of different hematological malignancies were diagnosed by immunophenotyping. Among 68 cases of early B-cell ALL, 22 cases with distinct immunophenotype was identified as immature B-cell ALL. Blasts from these ALL-B patients demonstrated prominent expression of CD10, CD19, CD22, but neither cytoplasmic nor surface IgM receptors. This strongly indicates leukemogenesis at an early stage of B-cell development. We also identified, the existence of a subpopulation of cells with remarkably similar phenotype in non-leukemic marrow from healthy subjects (expressing CD10, CD19, CD22, CD24, Tdt together with the co-expression of CD13). This sub-population of B cells concomitantly expressing CD13 appeared to be a highly proliferating group. By blocking their cell surface CD13 in leukemic blasts with monoclonal antibody we were able to inhibit their proliferation. We hypothesized that neoplastic transformation at this stage may be facilitated by CD13. CD13 may thus be an important target for novel molecular therapy of early stage acute B-cell leukemia.

Acute leukemia: Diagnosis improved by flow cytometry in addition to morphology

Aims:  Immunophenotyping using flow cytometry (FCM) has become an essential component of acute leukemia (AL) diagnosis. This study evaluated the judicious application of FCM as an adjunct to well‐informed morpho‐cytochemical assessment in patients with acute leukemia.

Leishmania donovani reduces the levels of retinoic acid–synthesizing enzymes in infected macrophages and favoring its own survival

AbstractPeople suffering from malnutrition become susceptible to the infection like Leishmania sp., as it results in a compromised immune response. Retinoic acid (RA), an important constituent of nutrition, shows an immune-modulatory activity. However, its role in the containment of infection is not yet ascertained, particularly in case of visceral leishmaniasis (VL). VL patients (n = 10) and healthy endemic controls (n = 9) were recruited to measure the serum levels of RA. An in vitro model of Leishmania infection using the murine mφ cell line J774.1 was used to investigate the RA-synthesizing enzymes (RALDH-1 and RALDH-2). Parasite loads among infected mφ were measured by quantitative expression of kDNA in the presence of an inhibitor of the RALDH-2 enzyme. We found a significant decrease in the serum levels of RA in VL cases. Importantly, we observed decreased levels of RALDH-1 and RALDH-2 among L. donovani–infected mφ along with simultaneous decrease as well as increase in the Th-1 and Th-2-associated factors, respectively. Furthermore, the pretreatment of mφ with an RALDH-2 inhibitor improved parasite in vitro infection. Our findings show impaired RA pathway among infected mφ and indicate that an intact RA pathway is critical for anti-Leishmania immune response. Graphical abstractᅟ

HIV induced suppression of host immunity: relevance to Mycobacterium tuberculosis infections

Compromised immunity among human immunodeficiency virus (HIV) infection attracts some of the most notorious opportunistic infections (OIs) like Mycobacterium tuberculosis etc. The increased burden of HIV tuberculosis (HIV-TB) cases also increases their transmission rate in the community. Chemotherapy presumably brings down the viral number below certain threshold number, which can be successfully contained by the host immune response. An impaired immunity, not only facilitates the dissemination of virus, but also fails to mount sufficient level of effector immune response to inhibit the OIs. In general, the outcome of the infection is decided by the equilibrium between the host’s effector immune response and extent of immune suppression, which facilitates immune evasion strategies evolved by the virus. During HIV infection, perturbation of immune homeostasis results from alteration in the representation of various fine T cell subsets, performing highly selective immune functions. This appears to have critical impact on effector T cell responses that keep the viral load under check and maintain latency of M. tuberculosis infection including other OIs. However, the precise role of these suppressor cells on the immune response among HIV infected individuals remains far from conclusive. Any alteration in frequency and function of these fine T cells that regulates the terminal effector response against latent M. tuberculosis infection, plausibly results in perturbation of immunity ending in reactivation of M. tuberculosis infection. The present review focuses the immunopathogenesis, immune suppression, and reactivation of M. tuberculosis among HIV infected patients. HIV AIDS Rev 2017; 16, 3: 140-154 DOI: https://doi.org/10.5114/hivar.2017.66899

Exonal switch down-regulates the expression of CD5 on blasts of acute T cell leukaemia

To date, CD5 expression and its role in acute T cell lymphoblastic leukaemia (T‐ALL) have not been studied closely. We observed a significant reduction in surface expression of CD5 (sCD5) on leukaemic T cells compared to autologous non‐leukaemic T cells. In this study, we have shown the molecular mechanism regulating the expression and function of CD5 on leukaemic T cells. A total of 250 patients suffering from leukaemia and lymphoma were immunophenotyped. Final diagnosis was based on their clinical presentation, morphological data and flow cytometry‐based immunophenotyping. Thirty‐nine patients were found to be of ALL‐T origin. Amplification of early region of E1A and E1B transcripts of CD5 was correlated with the levels of surface and intracellular expression of CD5 protein. Functional studies were performed to show the effect of CD5 blocking on interleukin IL‐2 production and survival of leukaemic and non‐leukaemic cells. Lack of expression of sCD5 on T‐ALL blasts was correlated closely with predominant transcription of exon E1B and significant loss of exon E1A of the CD5 gene, which is associated with surface expression of CD5 on lymphocytes. High expression of E1B also correlates with increased expression of cytoplasmic CD5 (cCD5) among leukaemic T cells. Interestingly, we observed a significant increase in the production of IL‐2 by non‐leukaemic T cells upon CD5 blocking, leading possibly to their increased survival at 48 h. Our study provides understanding of the regulation of CD5 expression on leukaemic T cells, and may help in understanding the molecular mechanism of CD5 down‐regulation.