Biology Reference
In-Depth Information
Table 4 Isolated cell models for studies of asthma-related processes in 1990
Model
Preferred stimulus
Response
PDE
Platelets
Collagen, ADP
Aggregation
3,2,5
Neutrophils
fMLP
ROS, LTB
4
, HNE, CD11b
4
Eosinophils
C5a
ROS, IL-5, LTC
4
, ECP
4
TNF
a
, IL-10, LTB
4
Monocytes
LPS
4
Basophils
Allergen
LTC
4
, His, PGD
2
, GMCSF
3,4,3/4
T-cells
Anti-CD3/CD28
IL-4, IL-5, IFN
g
, proliferation
3,4,3/4
Macrophages
LPS
TNF
a
3,4,3/4
Dendritic cells
3,4,3/4
Cell preparations from human origin were the preferred model system for characterising future
drug candidates. Cell populations were enriched from human blood by multi-step separation
procedures, which were optimised over the years and ended up in one-step magnetic cell sorting
or culture-derived cells
ROS
reactive oxygen species,
HNE
human neutrophil elastase
LPS
TNF
a
Monocytes (MCs) are the circulating precursor cells of macrophages. Before
the routine techniques for obtaining highly purified leukocyte populations by
elutriation and magnetic cell sorting were established (Gantner et al.
1997a
), less
sophisticated but highly time-consuming methods were used. MCs were obtained
from human blood by gradient centrifugation and the resulting mixture of 80%
lymphocytes and 20% MC could be investigated (Thompson et al.
1976
; Semmler
et al.
1993
). The alternative separation procedure was adherence to plastic dishes
and separation from non-adherent cells (Schade and Schudt
1993
). Upon stimula-
tion with lipopolysaccharides (LPS), MCs release a variety of proinflammatory
factors including hydrolytic enzymes, growth factors, lipid mediators, ROS and
cytokines. TNF
a
and the matrix-degrading enzymes such as matrix metallopro-
teases (MMPs) for collagen and elastin are prominent mediators of inflammation in
asthma, rheumatoid arthritis (RA) and COPD. Inhibition of TNF
a
generation in
human and mouse MCs was demonstrated to be effectively reduced by PDE4
inhibitors in 1993 (Semmler et al.
1993
; Schade and Schudt
1993
). MC PDE
composition was originally analysed by Thompson and a considerably homo-
geneous peak of PDE4 was revealed by chromatography (Thompson et al.
1976
).
A summary of isolated cell models as they were available at about 1990 to explore
asthma-related processes is given in Table
4
.
4.3 T-Cells, Macrophages and Dendritic cells for Dual
PDE Inhibitors
T cells release several cytokines which contribute to the inflammatory process in
various diseases such as asthma, RA, intestinal bowel disease (IBD), multiple
sclerosis (MS) or COPD. T-cell responses upon immunological stimulation such
as cell activation, cytokine secretion and clonal proliferation depend on the cAMP/
