IgG1 is pathogenic in Leishmania mexicana infection.

There are >2 million new cases of leishmaniasis annually, and no effective vaccine has been developed to prevent infection. In murine infection, Leishmania mexicana, which lives intracellularly in host macrophages, has developed pathways to hijack host IgG to induce a suppressive IL-10 response through FcγRs, the cell-surface receptors for IgG. To guide vaccine development away from detrimental Ab responses, which can accompany attempts to induce cell-mediated immunity, it is crucial to know which isotypes of IgG are pathogenic in this infection. We found that IgG1 and IgG2a/c induce IL-10 from macrophages in vitro equally well but through different FcγR subtypes: IgG1 through FcγRIII and IgG2a/c through FcγRI primarily, but also through FcγRIII. In sharp contrast, mice lacking IgG1 develop earlier and stronger IgG2a/c, IgG3, and IgM responses to L. mexicana infection and yet are more resistant to the infection. Thus, IgG1, but not IgG2a/c or IgG3, is pathogenic in vivo, in agreement with prior studies indicating that FcγRIII is required for chronic disease. This calls into question the assumption that macrophages, which should secrete IL-10 in response to IgG1 and IgG2a/c immune complexes, are the most important source of IL-10 generated by IgG-FcγR engagement in L. mexicana infection. Further investigations are required to better determine the cell type responsible for this immunosuppressive FcγRIII-induced IL-10 pathway and whether IgG2a/c is protective.

Single-dose pharmacokinetics and safety of HA-1A, a human IgM anti-lipid-A monoclonal antibody, in pediatric patients with sepsis syndrome.

The pharmacokinetics and safety of HA-1A (Nebacumab), a human IgM monoclonal antibody with specificity for the lipid A region of endotoxin, were evaluated in a multicenter trial of pediatric patients with sepsis syndrome or septic shock. Forty-two patients received a total of 44 infusions of drug, at a dose of 3 mg/kg (maximum 100 mg). The mean age was 7 years 10 months (range, 11 months to 16 years 7 months). The pharmacokinetic behavior of HA-1A during 36 hours was best described by a one-compartment open model. Clearance (6.1 +/- 2.0 ml/kg per hour) and apparent volume of distribution at steady state (0.11 +/- 0.03 L/kg) were larger than values reported previously in adults with sepsis syndrome. Elimination half-life (14.5 +/- 6.8 hours) and plasma concentration after infusion (30.7 +/- 14.5 mg/L) were similar to adults' values. In an additional three patients studied for 72 hours after administration, a biexponential function (i.e., two-compartment open model) best described the pharmacokinetic behavior of HA-1A: clearance (1.5 +/- 1.4 ml/hr per kilogram) and apparent volume of distribution at steady state (0.2 +/- 0.02 L/kg) were different (p < 0.002) from values observed in children's blood samples during 36 hours. Within the pediatric population, no age-related differences in pharmacokinetics could be detected. Drug disposition was unaffected by renal or hepatic dysfunction. Decreased blood pressure was the most frequently reported adverse event; 4 (9%) episodes in 44 infusions were considered possibly related to the study drug. Gram-negative bacteremia was documented in 23 (55%) of 42 patients. The overall mortality rate was 31%. Enterobacter cloacae was the most common pathogen isolated. Haemophilus influenzae type b was isolated from one child with sepsis syndrome. We conclude that infusion of HA-1A in children is associated with a low incidence of side effects. The pharmacokinetic-pharmacodynamic behavior of HA-1A in children requires further study to determine whether developmental differences exist and how these differences might affect drug administration. Efficacy remains to be studied.