Interleukin 12 deficiency associated with recurrent infections

Abstract

A 3-yr-old female patient exhibited interleukin 12 (IL-12) deficiency that was associated with recurrent episodes of pneumococcal pneumonia with sepsis and other infections in the absence of fevers. The patient's peripheral blood mononuclear cells (PBMCs) exhibited normal proliferative responses to antigens. Immune responses, including in vivo production of antibodies to diphtheria, tetanus, or pneumococcal antigens, were normal. Ig levels and B cell and T cell phenotypes were also normal. In contrast, IL-12 p70 heterodimer production was undetectable by using supernatants of the patient's stimulated PBMCs when compared with control cells treated similarly. Although present, interferon gamma (IFN-gamma) was reduced. The addition of recombinant IFN-gamma to control cells enhanced the production of IL-12 by up to sixfold. By contrast, IL-12 was undetectable in supernatants of the patient's cells in the presence of recombinant IFN-gamma. IL-12 p40 subunit mRNA by using the patient's PBMCs after stimulation with Staphylococcus aureus Cowan strain 1 or lipopolysaccharide was also undetectable by reverse transcription-PCR when compared with control cells. Production of IL-2, IL-6, tumor necrosis factor alpha, or IFN-gamma of the patient's PBMCs after appropriate stimulation was observed. This patient has either a defect in Staphylococcus aureus Cowan strain 1-lipopolysaccharide- or staphylococcal enterotoxin A-induced signaling pathways for the activation of IL-12 p40 gene expression, or an abnormality in the IL-12 p40 gene itself.

Figure 1

IL-12 p70 production in the presence of IFN-γ. PBMCs from the patient or control were incubated with SEA (10 ng/ml) or SAC (1:10,000, wt/vol) in the presence of IFN-γ at varying concentrations. The cultures were incubated for 24 h at 37°C, and the supernatants were then tested for IL-12 p70 production by ELISA.

Figure 2

(A) Expression of IL-12 p40 mRNA. PBMCs from the patient (KC) or from healthy controls were incubated with SAC or medium alone (experiment 1) or with LPS or medium alone (experiment 2) for 4 h. Next, total RNA was extracted, and reverse transcription–PCR was performed by using specific primers for human IL-12 p40 subunit or β-actin. The sizes of the PCR products for IL-12 p40 and β-actin are 465 bp and 510 bp, respectively. (B) Densitometric analysis of IL-12 p40 mRNA levels. The IL-12 p40 band densities were normalized to the corresponding β-actin densities and expressed as arbitrary optical density units (AODU). Results are representative of three separate experiments.