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The Mystery of Marginal Zone B Cells: Why Are They So Important?
In the complex network of the immune system, marginal zone B cells play a crucial role. These cells are not only the body's first line of defense against infection, but are also critical in the development of tumors. Mutations in marginal zone B cells may lead to various types of marginal zone lymphomas, and the treatment and prognosis of these lymphomas are affected by many different factors. This article will delve into the importance of marginal zone B cells and their associated lymphomas, as well as their role in the immune response.
Marginal zone B cells are natural lymphocytes that rapidly produce IgM antibodies against antigens.
Marginal zone lymphomas (MZLs) are a heterogeneous lymphoma caused by the malignant transformation of marginal zone B cells. These B cells are mainly located in mucosa-associated lymphoid tissue (MALT) and mature in the spleen and lymph nodes. In 2016, the World Health Organization classified these lymphomas into three types, namely peripheral marginal zone lymphoma (EMZL), splenic marginal zone lymphoma (SMZL), and nodal marginal zone lymphoma (NMZL). The progression and prognosis of each type of disease are quite different, making understanding MZL even more complex.
MZLs account for 5-17% of all non-Hodgkin lymphomas.
These marginal zone lymphomas mostly occur in elderly people over 65 years old, and most of them are less malignant diseases. In asymptomatic patients, a watchful waiting strategy may be adopted initially. However, the long-term prognosis of NMZL is generally not as good as other types, and in some cases, any MZL type can progress to more aggressive lymphomas, particularly diffuse large B-cell lymphoma. A distinctive feature of MZL is that their onset is associated with persistent stimulation by chronic infection or autoimmune disease.
Peripheral marginal zone lymphoma
Peripheral marginal zone lymphoma (EMZL) mainly invades MALT tissues, especially in the gastrointestinal tract. About 50-70% of EMZL cases originate from the stomach, while other organs such as the esophagus and small intestine are relatively rare. These lymphoma types are labeled as different subtypes based on the organ involved; for example, gastric EMZL is called primary gastric EMZL. Although the pathogenesis and histopathological characteristics of EMZL are similar, different subtypes have significant differences in clinical manifestations, progression, and treatment strategies.
Many cases of EMZL are associated with persistent stimulation of chronic inflammation and infection.
Pathophysiological characteristics
The development of EMZL is affected by many factors. The frequency of the disease increases if there is a history of blood cancers in the family, especially leukemia or various autoimmune diseases such as Sjögren's syndrome or lupus. Chronic inflammation is a key trigger factor affecting disease, because it prompts B cells to reorganize their immunoglobulin genes, leading to their abnormal response to disease antigens. Over time, these B cells may accumulate chromosomal abnormalities and genetic mutations, eventually malignantly transforming into EMZL.
Histopathological features
Histopathological examination of EMZL shows a vague nodular or diffuse cellular pattern. The morphology of malignant cells varies from case to case, including small to medium lymphocytes and large B cells. In these lesions, when large B cells form significant tissue, it may mean the disease is transitioning into the more aggressive form of diffuse large B-cell lymphoma. This transition occurs in about 18% of patients, on average 4 to 5 years after the original diagnosis.
Subtypes, diagnosis, treatment and prognosis
Different subtypes of EMZL occur primarily in mucosa-associated lymphoid tissue and are often named after primary EMZL (eg, primary gastric EMZL). However, about 30% of cases spread to other sites, mainly lymph nodes. The overall prognosis for these lymphomas is good, with five-year overall survival rates generally ranging from 86% to 95%. Primary gastric EMZL is the most common subtype, presents with low-grade malignancy, is usually accompanied by chronic Helicobacter pylori infection, and can be cured by treatment targeting this pathogen.
As research continues, we have a deeper understanding of marginal zone B cells and their role in the immune system. However, how many unknown secrets are waiting for us to explore in the future about these cells and their associated lymphomas?
