FcRn is a CD32a coreceptor that determines susceptibility to IgG immune complex-driven autoimmunity

IgG immune complexes (ICs) promote autoimmunity through binding fragment crystallizable (Fc) γ-receptors (FcγRs). Of these, the highly prevalent FcγRIIa (CD32a) histidine (H)-131 variant (CD32a^H) is strongly linked to human autoimmune diseases through unclear mechanisms. We show that, relative to the CD32a arginine (R)-131 (CD32a^R) variant, CD32a^H more avidly bound human (h) IgG1 IC and formed a ternary complex with the neonatal Fc receptor (FcRn) under acidic conditions. In primary human and mouse cells, both CD32a variants required FcRn to induce innate and adaptive immune responses to hIgG1 ICs, which were augmented in the setting of CD32a^H. Conversely, FcRn induced responses to IgG IC independently of classical FcγR, but optimal responses required FcRn and FcγR. Finally, FcRn blockade decreased inflammation in a rheumatoid arthritis model without reducing circulating autoantibody levels, providing support for FcRn’s direct role in IgG IC-associated inflammation. Thus, CD32a and FcRn coregulate IgG IC-mediated immunity in a manner favoring the CD32a^H variant, providing a novel mechanism for its disease association.

The Neonatal Fc Receptor (FcRn): A Misnomer?

Antibodies are essential components of an adaptive immune response. Immunoglobulin G (IgG) is the most common type of antibody found in circulation and extracellular fluids. Although IgG alone can directly protect the body from infection through the activities of its antigen binding region, the majority of IgG immune functions are mediated via proteins and receptors expressed by specialized cell subsets that bind to the fragment crystallizable (Fc) region of IgG. Fc gamma (γ) receptors (FcγR) belong to a broad family of proteins that presently include classical membrane-bound surface receptors as well as atypical intracellular receptors and cytoplasmic glycoproteins. Among the atypical FcγRs, the neonatal Fc receptor (FcRn) has increasingly gained notoriety given its intimate influence on IgG biology and its ability to also bind to albumin. FcRn functions as a recycling or transcytosis receptor that is responsible for maintaining IgG and albumin in the circulation, and bidirectionally transporting these two ligands across polarized cellular barriers. More recently, it has been appreciated that FcRn acts as an immune receptor by interacting with and facilitating antigen presentation of peptides derived from IgG immune complexes (IC). Here we review FcRn biology and focus on newer advances including how emerging FcRn-targeted therapies may affect the immune responses to IgG and IgG IC.

Host gene expression changes correlating with anti-HIV-1 effects in human subjects after treatment with peginterferon Alfa-2a

We investigated whether interferon-inducible genes (IFIGs) with known anti-human immunodeficiency virus (HIV) activity in vitro were associated with in vivo virological response in HIV infection. Nine untreated HIV-1-infected volunteers were treated for 12 weeks with peginterferon alfa-2a. A subset of IFIGs (23 of 47) increased compared with baseline through 6 weeks beyond therapy, and 10 of the 23 IFIGs significantly inversely correlated (r = -0.7; P < .05) with virological response. The strength of peginterferon alfa-2a-induced IFIG response significantly correlated with declines in HIV load during treatment (r(2) = 0.87, p = .003). This study links HIV virological response to a specific IFIG subset, a potential prognostic indicator in peginterferon alfa-2a-treated patients with HIV infection.

Chronic anti-phencyclidine monoclonal antibody therapy decreases phencyclidine-induced in utero fetal mortality in pregnant rats

Illicit drug use during pregnancy is a serious social and public health problem inflicting an array of deleterious effects on both mother and offspring. We investigated the hypothesis that a murine anti-phencyclidine (PCP) monoclonal antibody (mAb6B5; K(D)=1.3 nM) can safely protect mother and fetus from PCP-induced adverse health effects in pregnant rats. Pregnant Sprague-Dawley rats (n=4-5) were intravenously administered bolus injections of PCP (1mg/kg) on multiple days during pregnancy. They were also chronically treated with anti-PCP mAb6B5 at 45 mg/kg as a PCP antagonist. This dose provided one mAb-PCP binding site for every four PCP molecules. Therapeutic and safety study endpoints included pregnancy outcome (litter size, number of live vs. dead pups), maternal hemodynamic status and locomotor activity. Maternal hemodynamic changes (i.e., blood pressure and heart rate) and locomotor activity were measured in dams from gestation days 6-21 (one day antepartum) using a radiotelemetry-tracking device with a femoral arterial pressure catheter. This mAb6B5 treatment regimen significantly (p=0.008) reduced the number of PCP-induced in utero fetal deaths (odds ratio=3.2; 95%CI 1.3 to 7.9) and significantly (p<0.05) reduced acute PCP-induced maternal locomotor effects in the second trimester. Maternal hemodynamic responses to PCP were not significantly affected by mAb6B5 treatment. In conclusion, these data suggest that anti-PCP mAb treatments administered during pregnancy can safely protect a mother and her fetus(es) from PCP-related morbidity and mortality even when the mAb dose is too low to significantly prevent other PCP-induced maternal pharmacological effects.

Complications and outcomes of brown recluse spider bites in children

Brown recluse spider bites may cause severe local and systemic morbidity, but data regarding morbidity in children are limited. This study reviewed inpatient medical records (n = 26; 10 years) with a discharge diagnosis of "spider bite" from a tertiary pediatric hospital. The majority (85%) of children had an inflammatory response accompanying necrosis, usually with signs of secondary cellulitis (77%). Hemolytic anemia (50%), rhabdomyolysis (27%), and acute renal failure (12%) were the most prevalent systemic effects. Hemolytic anemia was bimodal in distribution relative to the time-of-onset of the bite (early, 2.2 ± 0.4; late, 6.9 ± 1.5 days postbite, respectively; P = .004). Although no fatalities occurred in the population, 65% of children had major morbidity, including wound complications requiring surgical care and acute orbital compartment syndrome. The findings emphasize the importance of anticipatory patient/family education for outpatients and careful monitoring for systemic morbidity in inpatients. Timely and appropriate supportive care should yield favorable outcomes in most cases.

The fate and function of therapeutic antiaddiction monoclonal antibodies across the reproductive cycle of rats

During preclinical development of neuroprotective antiaddiction therapeutic monoclonal antibodies (mAbs) against phencyclidine (PCP) and (+)-methamphetamine, we discovered novel, gestation stage-specific changes in mAb disposition spanning the entire reproductive cycle of female rats. Each pharmacological change was independent of mAb dose and antigen target but was precisely coincident with transitions between the gestational trimesters, parturition, and lactation periods of the female reproductive cycle. Whereas anti-PCP mAb6B5 terminal elimination half-life (t(1/2λz)) in nonpregnant females was 6.6 ± 1.6 days, the mAb6B5 t(1/2λz) significantly changed to 3.7 ± 0.4 days, then 1.4 ± 0.1 days, then 3.0 ± 0.4 days in the second trimester, third trimester, and postpartum periods, respectively (p < 0.05 for each change). Initially, these evolving changes in mAb6B5 clearance (3.3-fold), distribution volume (1.8-fold), and elimination half-life (4.7-fold) affected our ability to sustain sufficient mAb6B5 levels to sequester PCP in the bloodstream. However, understanding the mechanisms underlying each transition allowed development of an adaptive mAb-dosing paradigm, which substantially reduced PCP levels in dam brains and fetuses throughout pregnancy. These mAb functional studies also revealed that antidrug mAbs readily cross the placenta before syncytiotrophoblast barrier maturation, demonstrating the dynamic nature of mAb pharmacokinetics in pregnancy and the importance of maintaining maternal mAb levels. These studies provide the first preclinical pregnancy model in any species for chronic mAb dosing and could have important implications for the use of antibody therapies involving blood organ barriers (such as addiction) or other chronic diseases in women of childbearing age (e.g., irritable bowel diseases, multiple sclerosis, breast cancer, rheumatoid arthritis).

Association between mannan-binding lectin and impaired lung function in cystic fibrosis may be age-dependent

An association between mannan-binding lectin (MBL) status and severity of lung function impairment in cystic fibrosis (CF) has been found in several studies, but not in others. To explore the possible basis for discrepancies in the literature, we related both MBL and L-ficolin concentrations to lung function and examined the results in relation to the age of the patients. For patients under 15 years of age, those with MBL < 200 ng/ml had better lung function than those with MBL > 200 ng/ml [median forced expiratory volume in 1 s (FEV(1)), 99% versus 83%; P = 0.05]. For patients over 15 years of age, those with MBL < 200 ng/ml had poorer lung function than those with MBL > 200 ng/ml (median FEV(1), 44% versus 55%; P = 0.1). Also, for the over 15-year-olds, the proportion of patients with FEV(1) values below the median was greater in the MBL-insufficient subgroup (P < 0.04). In other words, relative deficiency of MBL appears to accelerate the age-related decline in lung function in CF patients. No corresponding relationships could be found between L-ficolin concentration and lung function. These findings and interpretation lend support to the potential value of MBL replacement therapy in a small minority of cystic fibrosis patients.

Competence in the context of adversity: pathways to resilience and maladaptation from childhood to late adolescence

Competent outcomes in late adolescence were examined in relation to adversity over time, antecedent competence and psychosocial resources, in order to investigate the phenomenon of resilience. An urban community sample of 205 (114 females, 90 males; 27% minority) children were recruited in elementary school and followed over 10 years. Multiple methods and informants were utilized to assess three major domains of competence from childhood through adolescence (academic achievement, conduct, and peer social competence), multiple aspects of adversity, and major psychosocial resources. Both variable-centered and person-centered analyses were conducted to test the hypothesized significance of resources for resilience. Better intellectual functioning and parenting resources were associated with good outcomes across competence domains, even in the context of severe, chronic adversity. IQ and parenting appeared to have a specific protective role with respect to antisocial behavior. Resilient adolescents (high adversity, adequate competence across three domains) had much in common with their low-adversity competent peers, including average or better IQ, parenting, and psychological well-being. Resilient individuals differed markedly from their high adversity, maladaptive peers who had few resources and high negative emotionality. Results suggest that IQ and parenting scores are markers of fundamental adaptational systems that protect child development in the context of severe adversity.