Intragastrical Inoculation Of Shiga-Toxin Producing Escherichia Coli (STEC) in Mice Immediately After Weaning Induce the Local Mucosal Immune Stimulation

ROMINA FERNANDEZ BRANDO; LETICIA BENTANCOR; MARÍA VICTORIA RAMOS; GABRIELA FERNÁNDEZ; MARIELA GONZÁLEZ; ROBERTO MEISS; MARTA RIVAS; MARINA PALERMO

Melbourne, Australia

Simposio; VTEC 2006. 6th International Symposium on Shiga Toxin (Verocytotoxin) Producing Escherichia coli Infections; 2006

The post diarrheal form of Hemolytic Uremic Syndrome is a rare but life-threatening complication of STEC infections in children. The existence of a specific and protective immune response to Shiga toxins (Stx) is controversial. As the first immune compartment is the mucosa associated lymphoid tissue, and Stxs may access the host by absorption across the intestinal epithelium, we investigated immune stimulation in Peyer’s Patches (PP) and mesenteric lymphoid nodes (MLN),  by studying  phenotypic alterations in lymphocytes after a sublethal inoculum of clinical isolates of STEC strains. Immature weaned mice were i.g. inoculated with 1 x 107 CFU of E. coli O157:H7 (Inoc), or saline as control (Ctrl), and after 24 hours and 7 days lymphocytes from PP and MLN were isolated. We evaluated T (CD3, CD4,CD8) and B (CD19) antigens and maturation/activation markers (CD25) using FITC/PE- stained specific antibodies and flow cytometry. We found a significantly lower percentage of B cells in PP and MLN, after 7 days of inoculation (PP: Ctrl= 74+4% vs Inoc= 60+7, p<0.03; MLN: Ctrl= 24+1 vs Inoc=14+2,p<0.005). This relative decrease in CD19+ cells was also evidenced as an enhanced CD3:CD19 ratio (PP: Ctrl=0.3+0.1 vs Inoc= 0.7+0.2, p<0.05; MLN: Ctrl= 3.1+0.1 vs Inoc=6.4+1.5, p<0.02). The total absolute number of B cells was selectively decreased (x103) (PP: Ctrl: 269.8+10.0 vs Inoc=131.1+13, p<0.01), while the absolute number of T cells was similar (x103) (PP: Ctrl=85.2+10 vs Inoc=98.9+13). The percentages of CD4+ and CD8+ T cells were conserved.  Inoculated mice showed the mean of fluorescence intensity of CD25 increased in T (p<0.04) and B cells (p<0.01) from PP at 24 hs post inoculum. We concluded that STEC induce a local T and B cell activation but also selectively eliminate B cells from mucosal lymphoid tissues. However, the elucidation of the mechanism and the bacterial components responsible for these effects needs further investigation.