TNF receptor superfamily member 13b (TNFRSF13B) hemizygosity reveals transmembrane activator and CAML interactor haploinsufficiency at later stages of B-cell development.

BACKGROUND: Heterozygous C104R or A181E TNF receptor superfamily member 13b (TNFRSF13B) mutations impair removal of autoreactive B cells, weaken B-cell activation, and convey to patients with common variable immune deficiency (CVID) an increased risk for autoimmunity. How mutant transmembrane activator and CAML interactor (TACI) influences wild-type TACI function is unclear; different models suggest either a dominant negative effect or haploinsufficiency. OBJECTIVE: We investigated potential TACI haploinsufficiency by analyzing patients with antibody-deficient Smith-Magenis syndrome (SMS) who possess only 1 TNFRSF13B allele and antibody-deficient patients carrying one c.204insA TNFRSF13B null mutation. METHODS: We tested the reactivity of antibodies isolated from single B cells from patients with SMS and patients with a c.204insA TNFRSF13B mutation and compared them with counterparts from patients with CVID with heterozygous C104R or A181E TNFRSF13B missense mutations. We also assessed whether loss of a TNFRSF13B allele induced haploinsufficiency in naive and memory B cells and recapitulated abnormal immunologic features typical of patients with CVID with heterozygous TNFRSF13B missense mutations. RESULTS: We found that loss of a TNFRSF13B allele does not affect TACI expression, activation responses, or establishment of central B-cell tolerance in naive B cells. Additionally, patients with SMS and those with a c.204insA TNFRSF13B mutation display normal regulatory T-cell function and peripheral B-cell tolerance. The lack of a TNFRSF13B allele did result in decreased TACI expression on memory B cells, resulting in impaired activation and antibody secretion. CONCLUSION: TNFRSF13B hemizygosity does not recapitulate autoimmune features of CVID-associated C104R and A181E TNFRSF13B mutations, which likely encode dominant negative products, but instead reveals selective TACI haploinsufficiency at later stages of B-cell development.

Ventilator weaning outcomes in chronic respiratory failure in children.

The purpose of this study was to describe mechanical ventilation weaning outcomes for children with chronic respiratory failure discharged from one of six post-acute rehabilitation facilities. Demographic, clinical and outcome data were collected from the medical record. Forty-four children were included in this prospective series; 20 (45%) were weaned off the ventilator at discharge. Children required significantly lower levels of ventilatory support at discharge than admission. Hourly use on the ventilator decreased from admission to discharge for the full cohort and for the subgroup who required a ventilator at discharge. Seventy-five percent of the children discharged with a ventilator had a portable unit. We conclude that nearly half of the children using mechanical ventilation achieve weaning during a postacute rehabilitation admission, whereas others have positive outcomes in severity, hours off the ventilator or portability of equipment.

Treatment of bronchomalacia in cystic fibrosis by silicone stent.

We report the case of a 15-year-old girl with cystic fibrosis and rapidly declining pulmonary function tests who was found to have collapse of the left main bronchus from bronchomalacia. She underwent successful deployment of an expandable silicone stent in the collapsed bronchus, after which her pulmonary function test results and her clinical picture markedly improved, obviating the need for immediate transplantation. A literature review yielded no prior reports of bronchomalacia in a cystic fibrosis patient being treated with a silicone stent. This case shows that a simple, effective treatment is possible for one cause of obstructive pulmonary function in cystic fibrosis.