Sialic acids siglec interaction A unique strategy to circumvent innate immune response by pathogens.

Sialic acids (Sias) are nine-carbon keto sugars primarily present on the terminal residue of cell surface glycans. Sialic acid binding immunoglobulins (Ig)-like lectins (siglecs) are generally expressed on various immune cells. They selectively recognize different linkage-specific sialic acids and undertake a variety of cellular functions. Many pathogens either synthesize or acquire sialic acids from the host. Sialylated pathogens generally use siglecs to manipulate the host immune response. The present review mainly deals with the newly developed information regarding mechanism of acquisition of sialic acids by pathogens and their biological relevance especially in the establishment of successful infection by impairing host innate immunity. The pathogens which are unable to synthesize sialic acids might adsorb these from the host as a way to engage the inhibitory siglecs. They promote association with the immune cells through sialic acids-siglec dependent manner. Such an association plays an important role to subvert host’s immunity. Detailed investigation of these pathways has been discussed in this review. Particular attention has been focused on Pseudomonas aeruginosa (PA) and Leishmania donovani.

Comparative analysis of differential expression of sialic acids and adhesion molecules on mononuclear cells of bone marrow and peripheral blood in childhood acute lymphoblastic leukaemia at diagnosis and clinical remission.

Childhood acute lymphoblastic leukaemia (ALL) is characterized by the neoplasm of immature haematopoietic precursor cells (HPCs). We report significant differences between the expression of sialoglycoproteins and adhesion molecules on mononuclear cells (MNCs) of bone marrow (BM) and peripheral blood (PB) from individual children at diagnosis of the disease. Lymphoblasts in PB predominantly expressed 9-O-acetylated sialoglycoproteins (Neu5,9Ac2-GPs), sialic acid, alpha2-3 linked sialic acid, L- and P-selectins and vascular cell adhesion molecule -1 (VCAM-1) on their surface compared to BM, as determined with selective lectins and monoclonal antibodies (mAbs) by flow cytometric analysis. CD34+CD38+ cells present either in diagnostic PB or BM always showed enhanced expression of both alpha2-3 and alpha2-6 linked sialic acids, Neu5,9Ac2-GPs, L- and P-selectins and VCAM-1, compared to CD34+CD38- population, as confirmed by higher mean fluorescence intensity (MFI). Expression of ICAM-1 was reverse. However, MFI of Neu5,9Ac2-GPs was always higher both in CD34+CD38+ and CD34+CD38- population in PB compared to BM. Diverse trend of these cell surface macromolecules was observed during clinical remission. This is the first comparative study between PB and BM, where significant differential distribution of sialylated macromolecules and adhesion molecules was observed. Hence, supervising these cell surface macromolecules at various stages of treatment might help in minimal residual disease detection, identifying mobilization factor(s) and in isolation of normal HPCs for autologous BM transplantation.

Glycobiology of Leishmania donovani.

Leishmania donovani, the causative organism of visceral leishmaniasis (VL) is one of the deadliest of the entire known Leishmania species. This protozoan parasite displays immense adaptability to survive under extremely harsh conditions. Cell surface glycoconjugates play a pivotal role in parasite virulence and infectivity. This review mainly highlights on the importance of these molecules and their reported roles with special emphasis on L. donovani sialobiology. The recently evolved information reported by our group regarding the identification and characterization of sialoglycans and their possible mode(s) of acquisition as also the detailed identification, characterization of anti-O-acetylated sialic acid (anti-OAcSA) antibodies and their emerging biological roles, notably as molecules that may aid in host defense against the pathogen has been vividly discussed in this review.

Antibodies against 9-O-acetylated sialic acids in childhood acute lymphoblastic leukemia: a two-year study with 186 samples following protocol MCP 943.

Initial studies have revealed an enhanced surface expression of 9-O-acetylated sialoglycoconjugates (9-OAcSGs) on lymphoblasts concomitant with high titers of antibodies (anti-9-OAcSGs) in childhood acute lymphoblastic leukemia (ALL). This study was undertaken in 186 coded samples from 69 ALL patients to evaluate if antibodies against these sialoglycans could monitor response to the treatment. An ELISA was developed using bovine submaxillary mucin (BSM) containing high % of 9-O-acetylated sialic acids (9-OAcSA) as the capture antigen, to investigate serum levels of anti 9-OAcSGs in a single-center series of pediatric, clinically-diagnosed and immunophenotypically confirmed ALL patients, as compared to 130 healthy controls. At presentation, a 3.8-fold increase in anti-9-OAcSGs levels was detected in 63/69 ALL patients (mean +/- SEM was 102.8 +/- 6.3 microg/ml) as compared to normal controls (27.17 +/- 0.76 microg/ml), assay sensitivity being 91.3%. On an individual basis (n = 25) in patients who were longitudinally monitored for two years, a significant decline in their mean +/- SEM of OD405 was observed from 0.85 +/- 0.06 to 0.28 +/- 0.03. Additionally, a dot-blot was developed to evaluate the proportion of immune-complexed 9-OAcSGs in these patients employing achatinin-H, a 9-OAcSA-binding lectin. Our data indicate that these economically viable ELISA-based approaches allow for reliable, sensitive and rapid diagnosis of ALL. We contend that these disease-specific antibodies could be considered as potential markers both for the initial diagnosis of ALL and possibly for longitudinal monitoring of the disease.