Escherichia coli enterotoxin modulates immunity but fails to prevent autoimmune hemolytic anemia in NZB mice

Background The B subunit of Escherichia coli heat-labile enterotoxin (EtxB) is a strong immunological modulator that enhances T helper-1 (Th1)-mediated autoimmune diseases. This study aimed to evaluate the effectiveness of inhaled EtxB in treating autoimmune hemolytic anemia (AIHA) in New Zealand Black (NZB) mice, which naturally develop AIHA. Methods Eight NZB mice received 20 µg of recombinant EtxB intranasally for four consecutive days, while the control group inhaled phosphate-buffered saline (PBS). 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. Hematocrit values were assessed at 12 weeks and 4 months 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) compared to PBS-treated controls. However, this difference was not maintained at 12 weeks ( 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 inhaling EtxB temporarily modulated the immune response at 6 weeks but did not sustain this effect beyond 12 weeks or prevent anemia.