Escherichia coli enterotoxin modulates humoral immune responses but fails to prevent autoimmune hemolytic anemia in NZB mice

Abstract Background The B subunit of Escherichia coli heat-labile enterotoxin (EtxB) is a strong immunological modulator that inhibits inflammatory responses associated with T helper-1 (Th1) by triggering immunological deviation pathways and shifting the immune response toward the Th2 profile. The objective of this study was to evaluate the effectiveness of inhaled EtxB in modulating humoral immune responses and treating autoimmune hemolytic anemia (AIHA) in New Zealand Black (NZB) mice, which naturally develop AIHA. Methods Eight female NZB mice at age of six weeks, received 20 µg of recombinant EtxB intranasally for four consecutive days, while six mice of the same sex and age inhaled phosphate-buffered saline (PBS) and served as the control group. The levels of total IgG, IgG1, and IgG2a antibodies bound to red blood cells (RBC) were measured by cellular ELISA at 6 and 12 weeks after EtxB inhalation. Hematocrit values were assessed at 12 weeks and 4 months after EtxB inhalation using a Hawksley Micro-hematocrit reader. Results After 6 weeks, EtxB-treated mice exhibited higher levels of RBC-bound IgG and IgG2a, along with a significantly lower IgG1/IgG2a ratio ( P 0.05), indicating a temporary immune modulation. EtxB did not delay the onset of anemia, as hematocrit readings showed no significant differences between groups at any time point ( P > 0.05). Conclusion This study demonstrated that EtxB inhalation temporarily modulated the humoral immune responses of NZB mice at 6 weeks, but this impact did not persist at 12 weeks and failed to prevent autoimmune hemolytic anemia in NZB mice.