Kyasanur Forest disease (KFD) is a tick-borne, acute, febrile viral illness endemic in southern India. No major studies have been done to understand the adaptive immune response during KFDV infection in humans. In this study, KFDV-positive patients were prospectively enrolled, and repeated peripheral blood collections were performed. Clinical and virologic characterization of these samples is reported along with phenotypic analysis of cellular immunity and quantitation of humoral immunity. We noted robust T and B cell responses, particularly of CD8 T cells, during KFDV infection in most of the patients. Virus clearance from the blood coincided with peak CD8 T cell activation and the appearance of KFDV-specific IgG. Increased frequency of plasmablasts and very few activated B cells were observed in the acute phase of KFD infection. Notably, only humoral immunity and activated B cell frequency in the acute phase correlated with prior KFDV vaccination, and only with 2 or more doses. This novel work has implications in KFD vaccine research as well as in understanding the pathogenesis.

Kyasanur 森林病 (KFD) 是一种蜱传的、急性的、发热的病毒性疾病，在印度南部流行。尚未进行重大研究来了解人类 KFDV 感染期间的适应性免疫反应。在这项研究中，前瞻性地招募了 KFDV 阳性患者，并进行了重复的外周血采集。报告了这些样品的临床和病毒学特征以及细胞免疫的表型分析和体液免疫的定量。我们注意到在大多数患者的 KFDV 感染期间，强烈的 T 和 B 细胞反应，特别是 CD8 T 细胞。从血液中清除病毒与峰值 CD8 T 细胞活化和 KFDV 特异性 IgG 的出现一致。在 KFD 感染的急性期观察到浆母细胞频率增加和很少活化的 B 细胞。尤其，只有急性期的体液免疫和活化 B 细胞频率与先前的 KFDV 疫苗接种相关，并且仅与 2 剂或更多剂相关。这项新工作对 KFD 疫苗研究以及了解发病机制具有重要意义。