Cathelicidin Antimicrobial Peptide Expression Is Inversely Associated with Absolute Neutrophil Counts in Pediatric HCT Recipients

• Published in: Blood 2019-11, Vol.134 (Supplement_1), p.3294-3294
• Main Authors: Domen, Jos, Yeh, Hung-Wen, Shreve, Nancy L, Sun, Lei, Li, Yongwu, Walters, Katrina D, Dalal, Jignesh, Goyal, Rakesh K.
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2019-131471

BACKGROUND: Neutropenia is a major risk factor for infectious complications in hematopoietic cell transplantation (HCT) recipients. However, much less is understood about neutrophil function in the posttransplant period. Cathelicidins are multifunctional host defense peptides. The sole human homolog, Cathelicidin Antimicrobial Peptide (CAMP, OMIM * 600474) is secreted by invading leukocytes, especially neutrophils and plays an important and pleiotropic role in host defense. It acts both as a direct bactericidal agent, but also affects the activity of many immune cells, including prolonging the lifespan of neutrophils. Another critical step in the microbicidal function of neutrophils is the generation of reactive oxygen species. OBJECTIVE: To characterize neutrophil function and CAMP expression over time in children following HCT. METHODS: A prospective study of children undergoing HCT was conducted. Blood samples were collected at 3 months, 6 mo., and 1 y post-HCT timepoints. White blood cells were purified using a PolymorphPrep gradient (Axis-Shield Diagnostics Ltd., Scotland). CAMP expression was measured using Clone H7 antibody (Santa Cruz Biotechnology Inc., USA) in fixed and permeabilized cells. Neutrophil activation was measured as reduction in membrane potential following stimulation with phorbol 12-myristate 13-acetate (PMA) using fluorescence staining with 3,3'-dipentyloxacarbocyanine iodide (DiOC5). Neutrophil hydrogen peroxide generation was measured by oxidation, and resultant increased staining of the probe 2',7' dichlorohydrofluorescein diacetate (DCFH-DA) following PMA stimulation. STATISTICS: Categorical variables were summarized by frequency and percent, and continuous variables were summarized by median and inter-quartile range (IQR). Distributions of continuous variables were examined and were log-transformed if skewed. Linear mixed-effects model was used to evaluate temporal trends and correlations between pairs of variables across time. points. The Bayesian Information Criterion was used to identify the optimal model that balanced model goodness-of-fit and complexity. RESULTS: Sixty-three patients were enrolled, median age 6.1 y (0.4 - 20.5 y). A majority of transplants (69%) were allogeneic. Patient and transplant characteristics are described in Table 1. CAMP was expressed in 95.8% of white blood cells (IQR 80.3 - 99.0%) (Figure 1). CAMP expression in neutrophils, measured as fold-increase above background staining, showed a median v