Human B-1 cells are important contributors to the naturally-occurring IgM pool against the tumor-associated ganglioside Neu5GcGM3

The Role of Non-Human Sialic Acid Neu5Gc-Containing Glycoconjugates in Human Tumors: A Review of Clinical and Experimental Evidence

N-Glycolylneuraminic acid (Neu5Gc) is a sialic acid variant commonly found in most mammals but not synthesized by humans due to an inactivating mutation in the CMP-Neu5Ac hydroxylase (CMAH) gene. Despite this, Neu5Gc-containing molecules are consistently detected in human tissues, particularly in malignant tumors. However, the mechanisms underlying Neu5Gc accumulation and its role in cancer development remain poorly understood.

OBJECTIVES

This review aims to analyze clinical and experimental evidence regarding the presence of Neu5Gc-containing glycoconjugates in both tumor and non-tumor human tissues, exploring potential mechanisms of the Neu5Gc expression and evaluating its contribution to tumor biology, with a particular focus on the Neu5Gc-GM3 ganglioside.

METHODS

A comprehensive review of the literature was conducted, integrating findings from immunohistochemistry, chromatography, and molecular studies to assess the expression and implications of Neu5Gc in cancer biology.

RESULTS

Neu5Gc-containing glycoconjugates were found to preferentially accumulate in various malignant tumors, while their presence in normal tissues was restricted to cells with high turnover rates. This accumulation is potentially mediated by dietary uptake, hypoxic conditions, and metabolic alterations in cancer cells. Additionally, Neu5Gc-containing molecules were associated with the activation of oncogenic pathways.

CONCLUSION

Neu5Gc-containing glycoconjugates play a multifaceted role in cancer progression and present potential as prognostic markers and therapeutic targets.

The immunology of B-1 cells: from development to aging

B-1 cells have intricate biology, with distinct function, phenotype and developmental origin from conventional B cells. They generate a B cell receptor with conserved germline characteristics and biased V(D)J recombination, allowing this innate-like lymphocyte to spontaneously produce self-reactive natural antibodies (NAbs) and become activated by immune stimuli in a T cell-independent manner. NAbs were suggested as "rheostats" for the chronic diseases in advanced age. In fact, age-dependent loss of function of NAbs has been associated with clinically-relevant diseases in the elderly, such as atherosclerosis and neurodegenerative disorders. Here, we analyzed comprehensively the ontogeny, phenotypic characteristics, functional properties and emerging roles of B-1 cells and NAbs in health and disease. Additionally, after navigating through the complexities of B-1 cell biology from development to aging, therapeutic opportunities in the field are discussed.

Peritoneal B1 and B2 cells respond differently to LPS and IL-21 stimulation

Peritoneal B cells can be divided into B1 cells (CD11b+CD19+) and B2 cells (CD11b-CD19+) based on CD11b expression. B1 cells play a crucial role in the innate immune response by producing natural antibodies and cytokines. B2 cells share similar traits with B1 cells, influenced by the peritoneal environment. However, the response of both B1 and B2 cells to the same stimuli in the peritoneum remains uncertain. We isolated peritoneal B1 and B2 cells from mice and assessed differences in Interleukin-10(IL-10) secretion, apoptosis, and surface molecule expression following exposure to LPS and Interleukin-21(IL-21). Our findings indicate that B1 cells are potent IL-10 producers, possessing surface molecules with an IgMhiCD43+CD21low profile, and exhibit a propensity for apoptosis in vitro. Conversely, B2 cells exhibit lower IL-10 production and surface markers characterized as IgMlowCD43-CD21hi, indicative of some resistance to apoptosis. LPS stimulates MAPK phosphorylation in B1 and B2 cells, causing IL-10 production. Furthermore, LPS inhibits peritoneal B2 cell apoptosis by enhancing Bcl-xL expression. Conversely, IL-21 has no impact on IL-10 production in these cells. Nevertheless, impeding STAT3 phosphorylation permits IL-21 to increase IL-10 production in peritoneal B cells. Moreover, IL-21 significantly raises apoptosis levels in these cells, a process independent of STAT3 phosphorylation and possibly linked to reduced Bcl-xL expression. This study elucidates the distinct functional and response profiles of B1 and B2 cells in the peritoneum to stimuli like LPS and IL-21, highlighting their differential roles in immunological responses and B cell diversity.

The role of B-1 cells in cancer progression and anti-tumor immunity

In recent years, in addition to the well-established role of T cells in controlling or promoting tumor growth, a new wave of research has demonstrated the active involvement of B cells in tumor immunity. B-cell subsets with distinct phenotypes and functions play various roles in tumor progression. Plasma cells and activated B cells have been linked to improved clinical outcomes in several types of cancer, whereas regulatory B cells have been associated with disease progression. However, we are only beginning to understand the role of a particular innate subset of B cells, referred to as B-1 cells, in cancer. Here, we summarize the characteristics of B-1 cells and review their ability to infiltrate tumors. We also describe the potential mechanisms through which B-1 cells suppress anti-tumor immune responses and promote tumor progression. Additionally, we highlight recent studies on the protective anti-tumor function of B-1 cells in both mouse models and humans. Understanding the functions of B-1 cells in tumor immunity could pave the way for designing more effective cancer immunotherapies.