Dipartimento di Scienze Mediche e Chirurgiche, UOC Gastroenterologia Fondazione Policlinico Universitario "A. Gemelli" IRCCS, Università Cattolica del Sacro Cuore, Rome, Italy.
Laboratorio di Patologia Clinica, Ospedale Madre Giuseppina Vannini, Rome, Italy.
Adv Clin Chem. 2022;108:155-209. doi: 10.1016/bs.acc.2021.08.002. Epub 2021 Sep 24.
Free light chain (FLC) kappa (k) and lambda (λ) consist of low molecular weight proteins produced in excess during immunoglobulin synthesis and secreted into the circulation. In patients with normal renal function, over 99% of FLCs are filtered and reabsorbed. Thus, the presence of FLCs in the serum is directly related to plasma cell activity and the balance between production and renal clearance. FLCs are bioactive molecules that may exist as monoclonal (m) and polyclonal (p) FLCs. These have been detected in several body fluids and may be key indicators of ongoing damage and/or illness. International guidelines now recommend mFLC for screening, diagnosis and monitoring multiple myeloma and other plasma cell dyscrasias. In current clinical practice, FLCs in urine indicate cast nephropathy and other renal injury, whereas their presence in cerebrospinal fluid is important for identifying central nervous system inflammatory diseases such as multiple sclerosis. Increased pFLCs have also been detected in various conditions characterized by B cell activation, i.e., chronic inflammation, autoimmune disease and HCV infection. Monitoring the coronavirus (COVID-19) pandemic by analysis of salivary FLCs presents a significant opportunity in clinical immunology worthy of scientific pursuit.
游离轻链（FLC）κ（k）和 λ（λ）由免疫球蛋白合成过程中过量产生的低分子量蛋白组成，并分泌到血液中。在肾功能正常的患者中，超过 99%的 FLC 被滤过并重吸收。因此，血清中 FLC 的存在与浆细胞活性以及产生和肾脏清除之间的平衡直接相关。FLC 是生物活性分子，可能以单克隆（m）和多克隆（p）FLC 的形式存在。这些已在几种体液中被检测到，可能是正在进行的损伤和/或疾病的关键指标。国际指南现在建议使用 mFLC 进行多发性骨髓瘤和其他浆细胞异常的筛查、诊断和监测。在当前的临床实践中，尿液中的 FLC 表明铸型肾病和其他肾脏损伤，而脑脊液中 FLC 的存在对于识别多发性硬化等中枢神经系统炎症性疾病很重要。在以 B 细胞激活为特征的各种情况下，也检测到了增加的 pFLC，即慢性炎症、自身免疫性疾病和 HCV 感染。通过分析唾液 FLC 监测冠状病毒（COVID-19）大流行在临床免疫学中提供了一个值得科学追求的重要机会。
