Low Levels of Immunoglobulins and Mannose-Binding Lectin Are Not Associated With Etiology, Severity, or Outcome in Community-Acquired Pneumonia

Abstract

BackgroundDisease severity and outcome in community-acquired pneumonia (CAP) depend on the host and on the challenge of the causal microorganism(s). We measured levels of immunoglobulins (Igs) and complement in 257 hospitalized adults with CAP and examined the association of low levels of Igs or complement to microbial etiology, disease severity, and short-term and long-term outcome.MethodsSerum Igs were analyzed in blood samples obtained at admission and at 6 weeks postdischarge if admission levels were low. Serum complement deficiencies were screened with a total complement activity enzyme-linked immunosorbent assay (ELISA), with further analyzes performed if justified. Disease severity was assessed by the CURB-65 severity score. Short-term outcome was defined as a composite end point of intensive care unit (ICU) admission and 30-day mortality, and long-term outcome as 5-year all-cause mortality.ResultsAt admission, 87 (34%) patients had low levels of at least 1 Ig, with low IgG2 as the most prevalent finding (55/21%). IgG levels were lower in bacterial than viral CAP (8.48 vs 9.97 g/L, P = .023), but low Igs were not associated with microbial etiology. Fifty-five (21%) patients had low lectin pathway activity, of which 33 (13%) were mannose-binding lectin (MBL) deficient. Low admission levels of any Ig or MBL were not associated with disease severity, short-term outcome, or long-term outcome. Excluding patients defined as immunocompromised from analysis did not substantially affect these results.ConclusionIn hospitalized adults with CAP, low admission levels of Igs or complement were in general not associated with microbial etiology, disease severity, short-term outcome, or long-term outcome.

Immunoglobulins concentration and B cell counts as severity markers in adult community-acquired pneumonia

“…On the other side, genetic conditioning of serum IgA levels in adults proposed by Dieguez et al [ 14 ] could explain the previous controversial publications with respect to IgA. [ 5 , 6 , 8 ]…”

“…Thus, while the Igs levels were similar in severe and mild cases defined by PSI or CURB65 or by severity parameters applied, B cells were lower in severe than mild patients. Our results about Igs levels agree with some reports, [ 8 ] but not with others, [ 11 ] and it hampers to present Igs levels as severity biomarkers.…”

“…[ 5 ] However, they disagree on the class/subclass of Igs compromised. [ 5 – 7 ] The use of antibodies level as a severity biomarker in these patients is also controversial, and while some studies found no relationship, [ 6 , 8 , 9 ] others have associated low IgG or IgA levels with severity and/or lethality. [ 5 , 10 , 11 ]…”

Clinical and laboratory associations of mannose-binding lectin in 219 adults with IgG subclass deficiency

“…In British adults with chronic obstructive pulmonary disease, the risk of infective exacerbations was significantly lower in patients with MBL2 genotypes that predicted low MBL levels [25]. In Norwegian adults hospitalized for treatment of community-acquired pneumonia, 13% had serum MBL < 50 ng/mL and 34% had subnormal serum Ig levels, but MBL < 50 ng/mL was not associated with specific causative microorganisms, severity of illness, or short- or long-term outcomes [28]. Taken together, these reports suggest that associations of low MBL levels and lower respiratory tract infection in cohorts of Caucasian adults unselected for subnormal total IgG or IgG subclasses vary according to specific infective microorganisms, the presence or absence of underlying lung disease, and serum Ig levels.…”