In 1860, H.H. Salter first noted the importance of bronchial smooth muscle contraction in asthma (1). Eighty years later, Kellaway et al. (2) recognized a distinctive bioactivity whose release following Ag challenge of sensitized lung elicited a contractile response that was slower in onset and more protracted than that elicited by histamine, the only known spasmogen of the time; they named this material “slow-reacting substance” (SRS). In 1960, W. Brocklehurst recognized that whereas histamine existed preformed, SRS was instead generated de novo during the Ag–Ab reaction, suggesting an enzymatic mechanism (3). These foundational observations sparked the quest to elucidate the chemical structure of SRS and its mechanism of biosynthesis—a quest that would ultimately require two more decades.

Although research by a number of laboratories around the world had provided certain methodologic and compositional clues to the identity of SRS, the data were ambiguous and progress was limited by the small quantities of biological material available for analysis. During the 1960s and 1970s, Samuelsson et al. (4) at the Karolinska Institute had accumulated substantial expertise in lipid structural analysis and the biochemistry of arachidonic acid oxygenation via cyclooxygenase and lipoxygenase pathways (5). This expertise would prove instrumental in solving the SRS puzzle, as described in the featured 1979 Pillars of Immunology article (6). R.C. Murphy, a visiting scientist working with the Samuelsson group, used calcium ionophore–stimulated mouse mastocytoma cells to generate sufficient quantities of spasmogenic SRS for analysis. This material incorporated isotopically labeled arachidonic acid and cysteine, and had four double bonds. Its UV absorption spectrum was consistent with that of a conjugated triene chromophore. As SRS was formed by leukocytes, they coined the term “leukotriene” (LT) and designated this structure LTC4. The cysteine-containing moiety was eventually determined to be the tripeptide glutathione, and SRS was subsequently revealed to represent a mixture of LTC4 plus two bioactive degradation products, LTD4 and LTE4, formed from the sequential removal of glutamic acid and glycine, respectively. As all three family members contained cysteine, these were collectively called cysteinyl LTs (cysLTs) (7). For this and other foundational work, Samuelsson was awarded the 1982 Nobel Prize for Physiology or Medicine.

Advances over the next two decades unraveled the biochemistry and cell biology of LT biosynthesis (812) and the pharmacologic characterization and cloning of the G protein–coupled CysLT1 receptor that mediates SRS contractile activity (13, 14). As prophesied by Brocklehurst in his Ph.D. thesis in 1958, the search for drugs inhibiting both the synthesis of (the 5-lipoxygenase inhibitor zileuton) and the receptor for (the CysLT1 antagonists zafirlukast, pranlukast, and montelukast) SRS came to fruition in the mid- to late-1990s (15). These agents not only represented the first example of an asthma therapy targeting a specific molecule (foreshadowing the development of targeted biologics such as anti–IL-5), but also the first new class of asthma therapy since corticosteroids, developed 40 years earlier. Together with studies of transgenic mice lacking specific enzymes or receptors (1618), clinical studies and experience with these drugs have provided a wealth of information about the spectrum of biological actions of cysLTs (19). We can now reflect on the lessons learned and whether the promise envisioned by Brocklehurst, and enabled by the findings reported in this Pillars of Immunology article, has been realized.

Indeed, it has been established that clinical benefit derives from blocking the potent contractile activity that gave SRS its name (20). However, this was just the tip of the iceberg. From the mid-1970s to the 1980s, it became apparent that the hyperresponsiveness of asthmatic airways was in part attributable to eosinophilic, or what is now termed type 2, inflammation (21), which in turn could be attenuated by inhaled corticosteroids (22). An unexpected revelation from the new molecular and pharmacologic tools for understanding cysLT actions was that these mediators could also promote type 2 responses (reviewed in Refs. 19 and 23) by enhanced recruitment, survival, or functional activation of dendritic cells (24, 25), eosinophils (26, 27), mast cells (28, 29), T cells (30, 31), B cells (32), and, more recently, type 2 innate lymphoid cells (33). The promotion of these processes in part reflects cysLT regulation of cytokine and cytokine receptor expression. CysLTs can also contribute to airway remodeling by promoting epithelial cell TGF-β generation (34), smooth muscle cell proliferation (35), fibroblast collagen synthesis (36), and fibrocyte migration and proliferation (37). Thus, cysLTs have the ability to phenocopy important actions of cytokines (e.g., modulation of inflammation) while also eliciting actions of which cytokines are incapable (e.g., smooth muscle contraction). Consequently, anti-LT agents have the potential to combine the benefits of a bronchodilator with those of an anti-inflammatory or “controller” agent—a profile of actions that otherwise requires treatment with inhaled corticosteroid plus bronchodilator; this combination remains unique among asthma treatments to this day. Moreover, although corticosteroids are often presumed to inhibit all aspects of inflammatory responses, it is notable that they have generally been found not to inhibit LT biosynthesis in vivo (38, 39); this may explain why in some patients an anti-LT drug can provide additive benefit to an inhaled corticosteroid. Indeed, oral anti-LT drugs are used today by millions of asthmatics and provide a unique profile of ease of use, efficacy, and safety.

On the other hand, the efficacy of anti-LT agents has not lived up to the high expectations that surrounded their development. This likely reflects limitations of existing drugs and of our ability to identify the patients who might benefit the most. First, zileuton inhibits in vivo LT synthesis by ∼50% (40). Second, at least two receptors for cysLTs in addition to CysLT1 are now recognized, and although their biologic roles remain incompletely defined, neither of these is blocked by currently available antagonists (41). Finally, heterogeneity in responses to existing anti-LT agents is well recognized (42), and although especially high urinary or sputum cysLT levels might identify patients most likely to benefit [examples include those suffering from aspirin-exacerbated respiratory disease (43) and the obese (44)], no large clinical trials have endeavored to prospectively select patients stratified by this biomarker. It is possible that application of precision approaches might identify a subset of more robust responders, as is now considered routine for other targeted therapies.

It is also worth noting that the potential landscape of pathologic states in which cysLTs may participate now also extends beyond asthma. For example, data support potential roles in tissue fibrosis (45), atherosclerosis (46), multiple sclerosis (47), and cancer (48, 49). However, a note of caution also applies, as cysLTs have been implicated not only in pathologic inflammation but also in innate immune defense against microbes (50).

The chemical identification of SRS reported in this featured Pillars of Immunology article and the related Nobel Prize awarded three years after its publication cast cysLTs and other lipid mediators at center stage. In the decades since, however, protein mediators such as cytokines and chemokines have gained undisputed hegemony as the dominant players in immunologic and inflammatory responses. Indeed, possible roles of lipid mediators or of the interactions between lipid and protein mediators in these responses are often not even considered. It is hoped that highlighting the discovery reported in this Pillars of Immunology article and the drug development it catalyzed will remind scientists that “unconscious bias” against lipid mediators limits our ability to discover immunologic truth and translate it for the benefit of patients.

Abbreviations used in this article:

cysLT

cysteinyl LT

LT

leukotriene

SRS

slow-reacting substance.

1
Salter
,
H. H.
1860
.
On Asthma: its Pathology and Treatment
.
Churchill
,
London
.
2
Kellaway
,
C. H.
,
E. R.
Trethewie
.
1940
.
The liberation of a slow-reacting smooth muscle-stimulating substance in anaphylaxis
.
Q. J. Exp. Physiol.
30
:
121
145
.
3
Brocklehurst
,
W. E.
1960
.
The release of histamine and formation of a slow-reacting substance (SRS-A) during anaphylactic shock
.
J. Physiol.
151
:
416
435
.
4
Samuelsson
,
B.
,
E.
Granström
,
K.
Green
,
M.
Hamberg
,
S.
Hammarström
.
1975
.
Prostaglandins
.
Annu. Rev. Biochem.
44
:
669
695
.
5
Borgeat
,
P.
,
B.
Samuelsson
.
1979
.
Transformation of arachidonic acid by rabbit polymorphonuclear leukocytes. Formation of a novel dihydroxyeicosatetraenoic acid
.
J. Biol. Chem.
254
:
2643
2646
.
6
Murphy
,
R. C.
,
S.
Hammarström
,
B.
Samuelsson
.
1979
.
Leukotriene C: a slow-reacting substance from murine mastocytoma cells
.
Proc. Natl. Acad. Sci. USA
76
:
4275
4279
.
7
Samuelsson
,
B.
1983
.
Leukotrienes: mediators of immediate hypersensitivity reactions and inflammation
.
Science
220
:
568
575
.
8
Matsumoto
,
T.
,
C. D.
Funk
,
O.
Rådmark
,
J. O.
Höög
,
H.
Jörnvall
,
B.
Samuelsson
.
1988
.
Molecular cloning and amino acid sequence of human 5-lipoxygenase
.
Proc. Natl. Acad. Sci. USA
85
:
26
30
.
9
Lam
,
B. K.
,
J. F.
Penrose
,
G. J.
Freeman
,
K. F.
Austen
.
1994
.
Expression cloning of a cDNA for human leukotriene C4 synthase, an integral membrane protein conjugating reduced glutathione to leukotriene A4
.
Proc. Natl. Acad. Sci. USA
91
:
7663
7667
.
10
Peters-Golden
,
M
.
1998
.
Cell biology of the 5-lipoxygenase pathway
.
Am. J. Respir. Crit. Care Med.
157
:
S227
S231
;
discussion S231–S222, S247–S228
.
11
Woods
,
J. W.
,
M. J.
Coffey
,
T. G.
Brock
,
I. I.
Singer
,
M.
Peters-Golden
.
1995
.
5-Lipoxygenase is located in the euchromatin of the nucleus in resting human alveolar macrophages and translocates to the nuclear envelope upon cell activation
.
J. Clin. Invest.
95
:
2035
2046
.
12
Mandal
,
A. K.
,
P. B.
Jones
,
A. M.
Bair
,
P.
Christmas
,
D.
Miller
,
T. T.
Yamin
,
D.
Wisniewski
,
J.
Menke
,
J. F.
Evans
,
B. T.
Hyman
, et al
.
2008
.
The nuclear membrane organization of leukotriene synthesis
.
Proc. Natl. Acad. Sci. USA
105
:
20434
20439
.
13
Drazen
,
J
.
1998
.
Clinical pharmacology of leukotriene receptor antagonists and 5-lipoxygenase inhibitors
.
Am. J. Respir. Crit. Care Med.
157
:
S233
S237
;
discussion S247–S238
.
14
Lynch
,
K. R.
,
G. P.
O’Neill
,
Q.
Liu
,
D. S.
Im
,
N.
Sawyer
,
K. M.
Metters
,
N.
Coulombe
,
M.
Abramovitz
,
D. J.
Figueroa
,
Z.
Zeng
, et al
.
1999
.
Characterization of the human cysteinyl leukotriene CysLT1 receptor
.
Nature
399
:
789
793
.
15
Drazen
,
J. M.
,
E.
Israel
,
P. M.
O’Byrne
.
1999
.
Treatment of asthma with drugs modifying the leukotriene pathway
.
N. Engl. J. Med.
340
:
197
206
.
16
Chen
,
X. S.
,
J. R.
Sheller
,
E. N.
Johnson
,
C. D.
Funk
.
1994
.
Role of leukotrienes revealed by targeted disruption of the 5-lipoxygenase gene
.
Nature
372
:
179
182
.
17
Kanaoka
,
Y.
,
A.
Maekawa
,
J. F.
Penrose
,
K. F.
Austen
,
B. K.
Lam
.
2001
.
Attenuated zymosan-induced peritoneal vascular permeability and IgE-dependent passive cutaneous anaphylaxis in mice lacking leukotriene C4 synthase
.
J. Biol. Chem.
276
:
22608
22613
.
18
Maekawa
,
A.
,
K. F.
Austen
,
Y.
Kanaoka
.
2002
.
Targeted gene disruption reveals the role of cysteinyl leukotriene 1 receptor in the enhanced vascular permeability of mice undergoing acute inflammatory responses
.
J. Biol. Chem.
277
:
20820
20824
.
19
Peters-Golden
,
M.
,
W. R.
Henderson
Jr.
2007
.
Leukotrienes
.
N. Engl. J. Med.
357
:
1841
1854
.
20
Montuschi
,
P.
,
M. L.
Peters-Golden
.
2010
.
Leukotriene modifiers for asthma treatment
.
Clin. Exp. Allergy
40
:
1732
1741
.
21
Barnes
,
P. J.
1989
.
New concepts in the pathogenesis of bronchial hyperresponsiveness and asthma
.
J. Allergy Clin. Immunol.
83
:
1013
1026
.
22
Djukanović
,
R.
,
J. W.
Wilson
,
K. M.
Britten
,
S. J.
Wilson
,
A. F.
Walls
,
W. R.
Roche
,
P. H.
Howarth
,
S. T.
Holgate
.
1992
.
Effect of an inhaled corticosteroid on airway inflammation and symptoms in asthma
.
Am. Rev. Respir. Dis.
145
:
669
674
.
23
Okunishi
,
K.
,
M.
Peters-Golden
.
2011
.
Leukotrienes and airway inflammation
.
Biochim. Biophys. Acta
1810
:
1096
1102
.
24
Okunishi
,
K.
,
M.
Dohi
,
K.
Nakagome
,
R.
Tanaka
,
K.
Yamamoto
.
2004
.
A novel role of cysteinyl leukotrienes to promote dendritic cell activation in the antigen-induced immune responses in the lung
.
J. Immunol.
173
:
6393
6402
.
25
Machida
,
I.
,
H.
Matsuse
,
Y.
Kondo
,
T.
Kawano
,
S.
Saeki
,
S.
Tomari
,
Y.
Obase
,
C.
Fukushima
,
S.
Kohno
.
2004
.
Cysteinyl leukotrienes regulate dendritic cell functions in a murine model of asthma
.
J. Immunol.
172
:
1833
1838
.
26
Suzuki
,
M.
,
M.
Kato
,
H.
Kimura
,
T.
Fujiu
,
A.
Morikawa
.
2003
.
Inhibition of human eosinophil activation by a cysteinyl leukotriene receptor antagonist (pranlukast; ONO-1078)
.
J. Asthma
40
:
395
404
.
27
Profita
,
M.
,
A.
Sala
,
A.
Bonanno
,
L.
Siena
,
M.
Ferraro
,
R.
Di Giorgi
,
A. M.
Montalbano
,
G. D.
Albano
,
R.
Gagliardo
,
M.
Gjomarkaj
.
2008
.
Cysteinyl leukotriene-1 receptor activation in a human bronchial epithelial cell line leads to signal transducer and activator of transcription 1-mediated eosinophil adhesion
.
J. Pharmacol. Exp. Ther.
325
:
1024
1030
.
28
Jiang
,
Y.
,
Y.
Kanaoka
,
C.
Feng
,
K.
Nocka
,
S.
Rao
,
J. A.
Boyce
.
2006
.
Cutting edge: Interleukin 4-dependent mast cell proliferation requires autocrine/intracrine cysteinyl leukotriene-induced signaling
.
J. Immunol.
177
:
2755
2759
.
29
Liu
,
T.
,
Y.
Kanaoka
,
N. A.
Barrett
,
C.
Feng
,
D.
Garofalo
,
J.
Lai
,
K.
Buchheit
,
N.
Bhattacharya
,
T. M.
Laidlaw
,
H. R.
Katz
,
J. A.
Boyce
.
2015
.
Aspirin-exacerbated respiratory disease involves a cysteinyl leukotriene-driven IL-33-mediated mast cell activation pathway
.
J. Immunol.
195
:
3537
3545
.
30
Spinozzi
,
F.
,
A. M.
Russano
,
S.
Piattoni
,
E.
Agea
,
O.
Bistoni
,
D.
de Benedictis
,
F. M.
de Benedictis
.
2004
.
Biological effects of montelukast, a cysteinyl-leukotriene receptor-antagonist, on T lymphocytes
.
Clin. Exp. Allergy
34
:
1876
1882
.
31
Prinz
,
I.
,
C.
Gregoire
,
H.
Mollenkopf
,
E.
Aguado
,
Y.
Wang
,
M.
Malissen
,
S. H.
Kaufmann
,
B.
Malissen
.
2005
.
The type 1 cysteinyl leukotriene receptor triggers calcium influx and chemotaxis in mouse alpha beta- and gamma delta effector T cells
.
J. Immunol.
175
:
713
719
.
32
Lamoureux
,
J.
,
J.
Stankova
,
M.
Rola-Pleszczynski
.
2006
.
Leukotriene D4 enhances immunoglobulin production in CD40-activated human B lymphocytes
.
J. Allergy Clin. Immunol.
117
:
924
930
.
33
Doherty
,
T. A.
,
N.
Khorram
,
S.
Lund
,
A. K.
Mehta
,
M.
Croft
,
D. H.
Broide
.
2013
.
Lung type 2 innate lymphoid cells express cysteinyl leukotriene receptor 1, which regulates TH2 cytokine production
.
J. Allergy Clin. Immunol.
132
:
205
213
.
34
Bossé
,
Y.
,
C.
Thompson
,
S.
McMahon
,
C. M.
Dubois
,
J.
Stankova
,
M.
Rola-Pleszczynski
.
2008
.
Leukotriene D4-induced, epithelial cell-derived transforming growth factor beta1 in human bronchial smooth muscle cell proliferation
.
Clin. Exp. Allergy
38
:
113
121
.
35
Panettieri
,
R. A.
,
E. M.
Tan
,
V.
Ciocca
,
M. A.
Luttmann
,
T. B.
Leonard
,
D. W.
Hay
.
1998
.
Effects of LTD4 on human airway smooth muscle cell proliferation, matrix expression, and contraction in vitro: differential sensitivity to cysteinyl leukotriene receptor antagonists
.
Am. J. Respir. Cell Mol. Biol.
19
:
453
461
.
36
Eap
,
R.
,
E.
Jacques
,
A.
Semlali
,
S.
Plante
,
J.
Chakir
.
2012
.
Cysteinyl leukotrienes regulate TGF-β(1) and collagen production by bronchial fibroblasts obtained from asthmatic subjects
.
Prostaglandins Leukot. Essent. Fatty Acids
86
:
127
133
.
37
Vannella
,
K. M.
,
T. R.
McMillan
,
R. P.
Charbeneau
,
C. A.
Wilke
,
P. E.
Thomas
,
G. B.
Toews
,
M.
Peters-Golden
,
B. B.
Moore
.
2007
.
Cysteinyl leukotrienes are autocrine and paracrine regulators of fibrocyte function
.
J. Immunol.
179
:
7883
7890
.
38
O’Shaughnessy
,
K. M.
,
R.
Wellings
,
B.
Gillies
,
R. W.
Fuller
.
1993
.
Differential effects of fluticasone propionate on allergen-evoked bronchoconstriction and increased urinary leukotriene E4 excretion
.
Am. Rev. Respir. Dis.
147
:
1472
1476
.
39
Mondino
,
C.
,
G.
Ciabattoni
,
P.
Koch
,
R.
Pistelli
,
A.
Trové
,
P. J.
Barnes
,
P.
Montuschi
.
2004
.
Effects of inhaled corticosteroids on exhaled leukotrienes and prostanoids in asthmatic children
.
J. Allergy Clin. Immunol.
114
:
761
767
.
40
Tagari
,
P.
,
C.
Brideau
,
C.
Chan
,
R.
Frenette
,
C.
Black
,
A.
Ford-Hutchinson
.
1993
.
Assessment of the in vivo biochemical efficacy of orally active leukotriene biosynthesis inhibitors
.
Agents Actions
40
:
62
71
.
41
Laidlaw
,
T. M.
,
J. A.
Boyce
.
2012
.
Cysteinyl leukotriene receptors, old and new; implications for asthma
.
Clin. Exp. Allergy
42
:
1313
1320
.
42
Malmstrom
,
K.
,
G.
Rodriguez-Gomez
,
J.
Guerra
,
C.
Villaran
,
A.
Piñeiro
,
L. X.
Wei
,
B. C.
Seidenberg
,
T. F.
Reiss
;
Montelukast/Beclomethasone Study Group
.
1999
.
Oral montelukast, inhaled beclomethasone, and placebo for chronic asthma. A randomized, controlled trial
.
Ann. Intern. Med.
130
:
487
495
.
43
Christie
,
P. E.
,
P.
Tagari
,
A. W.
Ford-Hutchinson
,
S.
Charlesson
,
P.
Chee
,
J. P.
Arm
,
T. H.
Lee
.
1991
.
Urinary leukotriene E4 concentrations increase after aspirin challenge in aspirin-sensitive asthmatic subjects
.
Am. Rev. Respir. Dis.
143
:
1025
1029
.
44
Giouleka
,
P.
,
G.
Papatheodorou
,
P.
Lyberopoulos
,
A.
Karakatsani
,
M.
Alchanatis
,
C.
Roussos
,
S.
Papiris
,
S.
Loukides
.
2011
.
Body mass index is associated with leukotriene inflammation in asthmatics
.
Eur. J. Clin. Invest.
41
:
30
38
.
45
Beller
,
T. C.
,
D. S.
Friend
,
A.
Maekawa
,
B. K.
Lam
,
K. F.
Austen
,
Y.
Kanaoka
.
2004
.
Cysteinyl leukotriene 1 receptor controls the severity of chronic pulmonary inflammation and fibrosis
.
Proc. Natl. Acad. Sci. USA
101
:
3047
3052
.
46
Di Gennaro
,
A.
,
D.
Wågsäter
,
M. I.
Mäyränpää
,
A.
Gabrielsen
,
J.
Swedenborg
,
A.
Hamsten
,
B.
Samuelsson
,
P.
Eriksson
,
J. Z.
Haeggström
.
2010
.
Increased expression of leukotriene C4 synthase and predominant formation of cysteinyl-leukotrienes in human abdominal aortic aneurysm
.
Proc. Natl. Acad. Sci. USA
107
:
21093
21097
.
47
Wang
,
L.
,
C.
Du
,
J.
Lv
,
W.
Wei
,
Y.
Cui
,
X.
Xie
.
2011
.
Antiasthmatic drugs targeting the cysteinyl leukotriene receptor 1 alleviate central nervous system inflammatory cell infiltration and pathogenesis of experimental autoimmune encephalomyelitis
.
J. Immunol.
187
:
2336
2345
.
48
Tsai
,
M. J.
,
P. H.
Wu
,
C. C.
Sheu
,
Y. L.
Hsu
,
W. A.
Chang
,
J. Y.
Hung
,
C. J.
Yang
,
Y. H.
Yang
,
P. L.
Kuo
,
M. S.
Huang
.
2016
.
Cysteinyl leukotriene receptor antagonists decrease cancer risk in asthma patients
.
Sci. Rep.
6
:
23979
.
49
Burke
,
L.
,
C. T.
Butler
,
A.
Murphy
,
B.
Moran
,
W. M.
Gallagher
,
J.
O’Sullivan
,
B. N.
Kennedy
.
2016
.
Evaluation of cysteinyl leukotriene signaling as a therapeutic target for colorectal cancer
.
Front. Cell Dev. Biol.
4
:
103
.
50
Peters-Golden
,
M.
,
C.
Canetti
,
P.
Mancuso
,
M. J.
Coffey
.
2005
.
Leukotrienes: underappreciated mediators of innate immune responses
.
J. Immunol.
174
:
589
594
.

The author has no financial conflicts of interest.