The immunomodulatory role of neutrophils and immune response to opportunistic fungi during neutropenia

Ref ID: 19424

Author:

L. Chai,1 J. Goh,1 L. Wu2 and W. J. Chng1

Author address:

1National University Health System, Singapore and 2Singapore
Immunology Network, Singapore

Full conference title:

6th Trends in Medical Mycology 2013

Date: 11 October 2014

Abstract:

Objectives Invasive fungal infection (IFI) is a major cause of mortal-
ity and morbidity in immunocompromised patients, of which Aspergillus
and Candida are the most common fungi. The recognition of
neutropenia as a risk factor for development of IFI underlies the role
which neutrophils play in mediating the host immune response to
opportunistic pathogens. Acute leukemia patients undergoing induc-
tion chemotherapy are at one of the highest risks in developing IFI.
To date, the immune status during febrile neutropenia remains not
well characterized. We aim to study the mechanism through which
neutrophils modulate response to fungal pathogens and the changes
in the net immune response through the state of neutropenia.
Methods From healthy volunteers, peripheral blood mononuclear
cells (PBMC) were separated by Ficoll density gradient centrifugation,
after which polymorphonuclear neutrophils (PMN) were isolated
from the erythrocyte fraction by hypotonic lysis. PBMC and PMN
were plated in 24-well Transwell plates at final concentration of
1 x 106/ml or 2 x 106/ml respectively in total volume of 1 ml in
RPMI culture medium. Stimulation was performed with Candida albicans
1×106/ml and Aspergillus fumigatus 1 x 106/ml. After 24 h and
48 h of incubation, supernatant were extracted from which individ-
ual cytokines were measured using ELISA.
Patients undergoing induction chemotherapy for acute myeloid
leukemia were recruited for the study with informed consent. Serial
blood specimens were obtained prior treatment, and at Weeks 1, 2, 3
and 4 post chemotherapy. Using whole blood, stimulations were per-
formed using A. fumigatus, C. albicans, Toll like receptor (TLR) 4
ligand Escherichia coli lipopolysaccharide and TLR2 ligand Pam3Cys.
At 24 h and 48 h, cytokine production was measured by ELISA.
Results Polymorphonuclear neutrophils by themselves did not
induce much cytokine response to Candida or Aspergillus. When co-
incubated with PBMC, PMN attenuated the production of tumour
necrosis factor alpha (TNFa) and interleukin 1 beta (IL-1b) to the
fungi. The use of the Transwell to effect separation between PBMC
and PMN partly reversed the attenuation on cytokine response, sug-
gesting that the phenomenon was dependent on secreted product as
well as PMN-PBMC contact. The effect could be replicated through
the addition of neutrophil myeloeroxidase to PBMC and Candida, but
not with arginase-1.
In patients undergoing induction chemotherapy, an enhanced
TNFa and IL-1b cytokine response to Candida and Aspergillus at Week
2 and Week 3 post commencement of chemotherapy. This coincided
with the periods of neutropenia.
Conclusions Neutrophils play an important role in attenuating the
immune response to fungal pathogens, mediated partly through
secreted myeloperoxidase and cellular contact. During febrile neutro-
penia, the absence of neutrophils results in an accentuated cytokine
milieu which may be implicated in the development of IFI.

Abstract Number: p211

Conference Year: 2013

Link to conference website: NULL

New link: NULL

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