A Transcriptional Defect Underlies B Lymphocyte Dysfunction in a Patient Diagnosed with Non-X-Linked Hyper-IgM Syndrome

Abstract

To establish the underlying cause of hyper-IgM syndrome in one female patient, B cell function was examined in response to CD40- and IL-4-mediated pathways. When CD40-induced functional responses were measured in unfractionated B cells, CD80 up-regulation, de novo Cμ-Cγ recombination, and Iγ transcription were all found to be relatively unaffected. However, CD40- and IL-4-mediated CD23 up-regulation and VDJ-Cγ transcription were clearly diminished compared to control cells. IL-4-induced CD23 expression was measurably reduced in the CD20− population as well. These results suggested that the patient’s defect is positioned downstream of CD40 contact and affects both CD40− and IL-4 signal transduction pathways. Further analysis of B cell function in CD19+ B cells revealed a clear B cell defect with respect to Iγ and mature VDJ-Cγ transcription and IgG expression. However, under the same conditions Iε transcription was relatively normal. Partial restoration of B cell function occurred if PBMC or CD19+ B cells were cultured in vitro in the presence of CD154 plus IL-4. Because addition of IL-4 to cocultures containing activated T cells failed to induce B cells to undergo differentiation, the ability of the patient’s B cells to acquire a responsive phenotype correlated with receiving a sustained signal through CD40. These findings support a model in which the patient expresses an intrinsic defect that is manifested in the failure of specific genes to become transcriptionally active in response to either CD154 or IL-4 and results in a functionally unresponsive B cell phenotype.

c-Rel plays a key role in deficient activation of B cells from a non–X-linked hyper-IgM patient

“…(C) Further analysis of the CD23b-II probe was performed with control D11 and pt1-LCL tet nuclear extracts. The following antibodies were added in increasing amounts to the indicated lanes: p50 (lanes 3-6), p65 (lanes 7-10), p52 (lanes [11][12][13][14], purified rabbit IgG (lanes 15-16), and c-Rel (lanes [17][18][19][20]. (D) EMSA with a probe that spans the identified NF-B binding site in the CD23a promoter (nucleotides Ϫ109 to Ϫ76).…”

“…on March 28, 2019. by guest www.bloodjournal.org From through CD40 and characterized by aberrant CD23 expression. 17 Further work revealed that pt1-LCLs initially expressed a CD23 lo / CD38 hi phenotype, yet over time, a predominant population of CD23 hi /CD38 lo cells with increased mitogenic activity emerged from the initial CD23 lo population. However, using pt1-LCL tet cells expressing LMP1 under the control of a tet-inducible promoter revealed that CD23 surface expression did not increase throughout culturing even though proliferation was driven efficiently by LMP1 signals (Lu et al 18 and K.T.L.…”

“…Unlike other HIGM B cells, defective GL transcription and CSR were capable of being complemented in vitro by extended signaling through CD40. 17 Also, there was a clear defect in cellular proliferation in response to mitogenic signals (K.T.L. and L.R.C., unpublished observation, August 2004).…”

“…7,[14][15][16] We have had a long-standing interest in defining the underlying mutation in a female patient (pt1) with undefined non-X-linked HIGM. 17 Previously, we reported that this patient has a defect in B-cell activation that specifically targeted a subset of CD40-induced responses, including selective impairment of CD23 expression. Unlike other HIGM B cells, defective GL transcription and CSR were capable of being complemented in vitro by extended signaling through CD40.…”

“…Together, these observations suggested that the pt1 mutation negatively affected the B cells' ability to respond to a normal threshold of CD40 activation signals resulting in antigen-dependent differentiation requiring a higher intensity of signaling ordinarily not achieved under physiological conditions. 17 Our most recent work has used a model system to further define the pt1 mutation. Specifically, a set of Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines (LCLs) was generated from pt1 and control B cells that express the viral transforming protein latent membrane protein 1 (LMP1) under the control of a tetracycline (tet)-inducible promoter (LCL tet ).…”