Background & aims The pathogenesis of chronic inflammatory bowel diseases (Crohn’s disease [CD] and ulcerative colitis) involves dysregulated TH1 and TH17 cell responses, which can be targeted therapeutically by the monoclonal antibody Ustekinumab directed against the joint p40 subunit of IL-12 and IL-23. These cytokines may also regulate the differentiation of T follicular helper (TFH) cells, which promote B cell function in germinal centers. However, the role of TFH cells in CD pathogenesis and impact of Ustekinumab therapy on TFH cell fate in patients are poorly defined. Methods Lymphocytes were isolated from peripheral blood (n=45) and intestinal biopsies (n=15) of CD patients or healthy controls (n=21) and analyzed by flow cytometry to assess TFH cell phenotypes and functions ex vivo . In addition, TFH cell differentiation was analyzed in the presence of Ustekinumab in vitro . Results TFH cell frequencies in the intestine as well as peripheral blood were associated with endoscopic as well as biochemical evidence of CD activity. CD patients with clinical response to Ustekinumab, but not those with response to anti-TNF antibodies, displayed reduced frequencies of circulating TFH cells in a concentration-dependent manner while the TFH phenotype was not affected by Ustekinumab therapy. In keeping with this notion, TFH cell differentiation was inhibited by Ustekinumab in vitro while TFH cell maintenance was not affected. Moreover, Ustekinumab therapy resulted in reduced germinal center activity in CD patients in vivo . Conclusions These data implicate TFH cells in the pathogenesis of CD and indicate that Ustekinumab therapy affects TFH cell differentiation, which may influence TFH-mediated immune functions in UST-treated CD patients.

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Zusammenfassung Bei 4 neurologischen Patienten kam es nach der Behandlung mit hochdosiertem intraven?sen Immunglobulin (IVIG) zu einem H?moglobin-(Hb-)Abfall um 2,7?4,1?g/dl; drei Patienten wurden dadurch transfusionsbed?rftig. Drei der 4?Patienten hatten einen positiven direkten Coombs-Test, bei allen 4?Patienten konnte Anti-A bzw. Anti-B im Eluat von Patientenerythrozyten nachgewiesen werden. Eine H?molyse durch das enthaltene Anti-A bzw. Anti-B ist eine zwar bekannte, m?glicherweise aber untersch?tzte Nebenwirkung der Behandlung mit hochdosiertem IVIG. Als Konsequenz empfehlen wir engmaschige Blutbildkontrollen w?hrend und nach der Gabe von hochdosiertem IVIG.