Non-Proliferative Immune Restoration by Euglena gracilis EK Powder in Cyclophosphamide-Induced Immunosuppressed Mice.

Cytotoxic chemotherapy frequently induces immunosuppression, impairing the innate cellular and humoral immune responses. Therefore, immunomodulatory agents that restore immune function without indiscriminate leukocyte expansion are required. This study examined whether Euglena gracilis EK powder (EKP), a paramylon-rich β-1,3-glucan preparation, supports immune recovery under cyclophosphamide (CPA)-induced immunosuppression. Male BALB/c mice received EKP (80, 200, or 500 mg/kg/day for 21 days) under a dual-temporal CPA design: acute phase (days 7 and 9) and established phase (days 14 and 17). The immune status was assessed using peripheral hematology, splenocyte viability, cytokine profiling, natural killer (NK) cell-associated activity, serum immunoglobulin levels, and splenic histopathology. EKP did not restore the peripheral leukocyte counts in either model, indicating that its immunological effects were independent of hematopoietic recovery. However, EKP treatment improved the levels of functional immune markers in a dose-dependent manner. EKP increased basal splenocyte viability without enhancing mitogen-induced proliferation, restored IFN-γ and TNF-α production, and suppressed excessive IL-6 levels. NK cell-associated activity recovered across all EKP doses (p < 0.05-0.01), consistent with the increase in IL-12 p70 levels at the highest dose. Serum IgG levels were restored at all doses (p < 0.05-0.01); however, IgM and IgA showed class-specific recovery at 200 and 500 mg/kg, respectively, with IgA recovery suggesting possible gut-associated lymphoid tissue involvement. Splenic histopathology confirmed the dose-dependent recovery of white pulp organization and germinal center formation. These findings support a framework wherein EKP improves immune functional markers by preserving existing immune components and cytokine rebalancing, rather than increasing circulating leukocytes.