High levels of catalytic antibodies correlate with favorable outcome in sepsis

Abstract

Sepsis is the leading cause of death in intensive care units and results from a deleterious systemic host response to infection. Although initially perceived as potentially deleterious, catalytic antibodies have been proposed to participate in removal of metabolic wastes and protection against infection. Here we show that the presence in plasma of IgG endowed with serine protease-like hydrolytic activity strongly correlates with survival from sepsis. Variances of catalytic rates of IgG were greater in the case of patients with severe sepsis than healthy donors (P < 0.001), indicating that sepsis is associated with alterations in plasma levels of hydrolytic IgG. The catalytic rates of IgG from patients who survived were significantly greater than those of IgG from deceased patients (P < 0.05). The cumulative rate of survival was higher among patients exhibiting high rates of IgG-mediated hydrolysis as compared with patients with low hydrolytic rates (P < 0.05). An inverse correlation was also observed between the markers of severity of disseminated intravascular coagulation and rates of hydrolysis of patients' IgG. Furthermore, IgG from three surviving patients hydrolyzed factor VIII, one of which also hydrolyzed factor IX, suggesting that, in some patients, catalytic IgG may participate in the control of disseminated microvascular thrombosis. Our observations provide the first evidence that hydrolytic antibodies might play a role in recovery from a disease.

Fig. 1.

Hydrolytic activity of IgG from septic patients. IgG was purified from plasma of 34 septic patients (circles) and 10 healthy donors (squares). Ten patients died within 28 days after diagnosis (filled circles), and 24 patients survived (open circles). To measure hydrolytic activity, IgG was incubated with PFR-MCA and fluorescence of released MCA quantitated. Spontaneous hydrolysis that occurred upon incubation of PFR-MCA in buffer alone was subtracted in all cases, thus yielding some negative values. *, Patients' IgG with rates greater than the mean catalytic activity of IVIg ± 2 SD (i.e., 113.5 μmol/min per mol).

Fig. 2.

High rates of IgG-mediated hydrolysis correlate with survival. Patients with sepsis were ranked according to the rates of hydrolysis of PFR-MCA exhibited by IgG purified from their plasma and divided into two groups based on the median catalytic activity of IgG. Cumulative rates of survival of patients with low catalytic rates (dotted line curve) differed significantly from those of patients with high catalytic rates (full line curve), as assessed in a Kaplan–Meier analysis (log-rank test, P < 0.05).

Fig. 3.

Correlation of rates of IgG-mediated hydrolysis with markers of disseminated intravascular coagulation. The patients were ranked according to the rates of IgG-mediated PFR-MCA hydrolysis and grouped into quartiles. Odd risk (OR) ratios were calculated for each quartile as the number of deceased patients over that of surviving patients, and are indicated as empty circles. Mean ± SEM of the prothrombin time (PT, expressed as the percentage of the clotting time measured with reference to a standard plasma, empty bars) and the activated partial thromboplastin time (aPTT, expressed as the ratio of the scored value to a reference value, full bars) as determined at the time of diagnosis of sepsis, are represented (eight or nine patients per quartile). PT values exhibited a significant correlation with hydrolysis rates of patients' IgG (P < 0.05, Spearman's rank correlation test using the ungrouped data). aPTT values displayed a tendency for significant correlation with rates of hydrolysis of patients' IgG (P < 0.1).

Fig. 4.

Hydrolysis of factors IX and VIII by patients' IgG. Human recombinant factor IX (FIX) and VIII (FVIII) were incubated in the presence of purified IgG for 24 h at 37°C. Migration profiles are shown for 14 representative patients. Mean optical densities of the migration profiles are indicated as arbitrary units (A.U.) for six surviving patients with high rates of IgG-mediated hydrolysis (thick line curve), four surviving patients with low rates, and four deceased patients (thin line curves). Coagulation proteins incubated in buffer alone (Ctl) or in the presence of IVIg (data not shown) were used as negative controls. Patients' IgG hydrolyzed neither HSA nor prothrombin (data not shown).