Epidemiology : in North
America the reported incidence of TRALI is
1/5000–1/1323 transfusionsref1,
ref2,
ref3.
The incidence in Europe is markedly lower, 1/7980, but the true incidence
of TRALI remains unknown, and it is unlikely to be determined until a consensus
definition can be reached
ref.
Aetiology : although no specific patient groups
are predisposed to TRALI, Van Buren et al first postulated that the clinical
status of the patient played a significant role in the genesis of TRALI
ref.
In a retrospective series of 10 TRALI patients compared to 10 patients
with uncomplicated febrile or urticarial transfusion reactions, investigators
hypothesized that TRALI was the result of 2 independent insults because
every patient in the TRALI group (10/10) had an antecedent "first event"
(such as recent major surgery, active infection, or massive transfusion);
only 2/10 patients in the control group had such a predisposing clinical
condition
ref.
These first events may have predisposed these patients to TRALI through
activation of the pulmonary endothelium resulting in neutrophil sequestration
in the lungs
ref.
Transfusion represented the second event that activated the PMNs in the
lung causing endothelial damage and capillary leak, culminating in TRALI
ref.
A prospective, epidemiologic study demonstrated that 2 patient groups were
at particular risk for developing TRALI, those patients in the induction
phase of treatment for hematological malignancies and patients with cardiovascular
disease who required
bypass
surgery
ref.
A recent report implicated massive transfusion as a risk factor for TRALI
in patients receiving
solid
organ transplants
ref.
Moreover, follow-up information from the Mayo Clinic group in their series
of 36 TRALI patients revealed that all of these patients had had recent
surgery
ref1,
ref2.
In addition, 2 other patient groups appear to be at risk for TRALI, patients
receiving
fresh
frozen plasma
for coumadin reversal and patients with
thrombotic
thrombocytopenic purpura (TTP)
who have widespread endothelial cell activation (personal communications
from Patricia M. Kopko, MD and Richard Benjamin, MD). In published series
of TRALI, plasma-containing blood components are most commonly implicated,
with whole blood–derived platelet concentrates (WB-PLTs) having caused
the largest number of these reactions
ref1,
ref2
(Popovsky MA. Transfusion related acute lung injury. In: Popovsky MA, ed.
Transfusion Reactions. Bethesda, MD: AABB Press; 2001). Although
the plasma fraction of blood or blood components rather than the cellular
constituents appears to be etiologic in TRALI, 2 of the most frequently
implicated products (WB-PLTs and PRBCs) do not contain large amounts of
plasma. Blood products implicated in TRALI listed in the order of numbers
of published cases :
-
whole blood–derived platelet concentrates (WB-PLTs)
-
fresh frozen
plasma (FFP)

-
packed red blood cells (PRBCs)
-
whole blood (WB)
-
apheresis platelet concentrates (A-PLTs)
-
granulocytes
-
stem cell preparations
-
intravenous gamma globulin
-
cryoprecipitate
Pathogenesis : 2 basic
mechanisms have been proposed for the pathogenesis of TRALI. The first
hypothesis is that TRALI is antibody-mediated and is caused by either the
passive infusion of donor antibodies directed against recipient antigens
or the infusion of donor leukocytes into a recipient who has antibodies
directed against these donor leukocytes
ref
(Popovsky MA. Transfusion related acute lung injury. In: Popovsky MA, ed.
Transfusion Reactions. Bethesda, MD: AABB Press; 2001). The second hypothesis
is that TRALI is caused by at least two independent events
ref1,
ref2,
ref3,
ref4.
The first event relates to the underlying clinical condition of the patient
such that this individual has pulmonary endothelial activation resulting
in pulmonary sequestration of neutrophils
ref1,
ref2,
ref3,
ref4.
The second event is the infusion of specific antibodies, directed against
the adherent PMNs in the lung, or other biologic response modifiers (including
lipophilic compounds) that cause activation of these primed, adherent PMNs
resulting in activation of the microbicidal arsenal of PMNs leading to
endothelial damage, capillary leak, and acute lung injury
ref1,
ref2,
ref3,
ref4.
-
antibody-mediated TRALI due to HLA class I and antigranulocyte antibodies
: in 1985, Popovsky and Moore proposed the infusion of donor antibodies
to explain TRALIref.
They documented donor antibodies to granulocytes in 89% of these cases
and antibodies to HLA antigens in 72% of cases examinedref.
Most of the granulocyte antibodies did not exhibit specificity, but 59%
of the HLA class I antibodies didref.
These findings have been confirmed by a number of other groups, and approximately
50% of donor antileukocyte antibodies display specific reactivity to recipient
antigensref1,
ref2,
ref3
(Popovsky MA. Transfusion related acute lung injury. In: Popovsky MA, ed.
Transfusion Reactions. Bethesda, MD: AABB Press; 2001). The infusion of
leukoagglutinins is postulated to cause complement activation resulting
in PMN influx into the lung followed by activation of these PMNs and release
of cytotoxic agents, resulting in endothelial damage, capillary leak and
pulmonary damageref1,
ref2
(Popovsky MA. Transfusion related acute lung injury. In: Popovsky MA, ed.
Transfusion Reactions. Bethesda, MD: AABB Press; 2001). In addition, TRALI
can be caused by the binding of recipient antibodies to discrete antigens
on transfused donor granulocytes; however, the number of viable PMNs is
an issue and such a mechanism represents only 10% of TRALI casesref
(Popovsky MA. Transfusion related acute lung injury. In: Popovsky MA, ed.
Transfusion Reactions. Bethesda, MD: AABB Press; 2001). Importantly, this
mechanism has particular relevance to patients receiving granulocyte transfusions
and must be taken into account for these individualsref
-
animal models of antibody-mediated TRALI : the relevance of these observations
was reported in an ex vivo rabbit model of TRALI in which lungs
were isolated from rabbits and perfused with human PMNs, antibodies directed
against specific PMN antigens or not, and rabbit plasma as a complement
source. These experiments demonstrated that acute lung injury, characterized
by severe pulmonary edema, resulted from the infusion of a mixture of human
PMNs [HNA-3a+ (5b+)], human HNA-3a antibodies, and
a complement sourceref.
In this ex vivo model pulmonary edema occurred 3–6 hours following
the infusion of the admixtureref.
However, if any one of the three components were deleted pulmonary edema
did not occurref.
Furthermore, if immunoglobulins with indeterminate antigen specificity
were infused together with complement and human PMNs, lung injury was not
observedref.
Recently, Bux et al have demonstrated that employing anti-granulocyte antibodies
and PMNs that have the cognate antigens may cause pulmonary edema without
the addition of a complement sourceref.
Although antibodies to HLA class I or granulocyte antigens explain many
TRALI cases, a number of problems with this mechanism remain. In the original
description, only 59% of the immunoglobulins identified demonstrated antigen
specificity and in published series of TRALI only about 50% of the implicated
antibodies demonstrate specificity for recipient antigensref
(Popovsky MA. Transfusion related acute lung injury. In: Popovsky MA, ed.
Transfusion Reactions. Bethesda, MD: AABB Press; 2001). Since such "non-specific
antibodies" did not cause TRALI in the ex vivo animal model, the
significance of these immunoglobulins, especially in the context of TRALI,
is undefinedref.
The precise mechanism for antibody-mediated TRALI is not known; moreover,
there are a number of cases of TRALI in which an antibody either in the
donor or in the recipient is not present, and recently a case of autologous
TRALI has been reportedref1,
ref2,
ref3,
ref4
(Popovsky MA. Transfusion related acute lung injury. In: Popovsky MA, ed.
Transfusion Reactions. Bethesda, MD: AABB Press; 2001).
-
TRALI secondary to the infusion of class II HLA antibodies : recently Kopko
et al postulated that TRALI is due to the infusion of HLA class II antibodies
with specificity for class II antigens in the recipient, and these findings
have been confirmedref1,
ref2,
ref3.
Furthermore, Kopko et al demonstrated in vitro that HLA class II antibodies
implicated in TRALI could activate circulating monocytes that expressed
these antigens causing synthesis of significant amounts of TNF-a,
IL-1ß and tissue factor over a 4-hour time period as compared to
monocytes incubated with control seraref.
In addition, because HLA class II antigens also are expressed on endothelial
cells, these investigators questioned whether infusion of class II antibodies
into a recipient with cognate antigen expression on the pulmonary endothelium
could manifest TRALI due to endothelial activation, changes in cellular
shape, fenestration, and capillary leakref.
The infusion of class II HLA antibodies into patients who express the cognate
antigens represents an attractive model for TRALI but raises a number of
questions. First, although the synthesis of cytokines by circulating monocytes
is interesting, there is a significant time delay for the production of
these inflammatory mediators; moreover, in these studies these cytokines
were intracellular and were not released into the supernatantref.
Second, this model has relevance only if the infused antibody specifically
recognizes a recipient antigenref.
-
the 2-event model of TRALI : all proposed models of TRALI implicate the
PMN as the effector cell, and both TRALI and ARDS are clinically identicalref1,
ref2,
ref3,
ref4,
ref5,
ref6.
Thus, it is important to understand PMN physiology, especially the interaction
of PMNs with pulmonary vascular endothelium and PMN-mediated cell damage
leading to acute lung injury. Moreover, the underlying clinical condition
of the patient is important as demonstrated in three "look back" studies;
those of Van Buren with a donor with HNA-2b antibodies, Kopko with a donor
with HNA-3a antibodies and Toy with a donor with multiple HLA class I and
II antibodiesref1,
ref2.
These studies demonstrated that the majority of transfused patients did
not develop TRALI even though their leukocytes contained the cognate antigensref1,
ref2.
In response to an infection in the tissues, inflammatory signals diffuse
to the vasculature and activate the vascular endothelium causing release
of chemokines, which attract PMNs to the endothelial surface. Attraction
is followed by selectin-mediated PMN rolling and ß2-integrin:ICAM-1
mediated firm adhesion of PMNs to endothelial cells (ECs)ref.
These PMNs, which have undergone a change from a non-adhesive to an adhesive
phenotype are now primedref1,
ref2.
Priming of PMNs enhances the microbicidal function of PMNs to a subsequent
stimulus and changes the activity of PMNs such that stimuli that normally
do not cause activation of quiescent neutrophils are able to activate primed
PMNsref1,
ref2.
It is important to note that priming is part of the orderly process of
PMN transmigration to the tissues, and although there are benefits to enhanced
PMN function including efficient destruction of pathogens, it is clear
priming may be detrimental to the host leading to PMN-mediated organ injury,
especially ARDS
ref1,
ref2.
The PMNs then diapedese through the endothelial layer, chemotax to the
site of infection and phagocytize. If the orderly process of PMN transmigration
is altered by a stimulus coming from the intravascular space rather than
the tissues, these intravascular stimuli activate vascular endothelial
cells (ECs) and cause attraction, firm adhesion and priming of PMNs. As
shown the vascular endothelium is activated causing the release of chemokines
that attract PMNs to the endothelial surface followed by selectin-mediated
tethering and firm adhesion through the ICAM-1:ß2-integrin
interaction. However, since there are not signals to cause diapedesis and
PMN chemotaxis into the tissues, the PMNs become sequestered, and these
primed, hyper-reactive leukocytes may be activated by stimuli that normally
have no effect including antibodies directed against specific leukocyte
antigens or the lipids that accumulate during routine storage of cellular
blood components. Activation of these adherent PMNs causes endothelial
damage, capillary leak, and organ injuryref.
-
during routine storage of cellular components, an effective PMN priming
activity accumulates that is lipophilic as determined by its solubility
in chloroformref1,
ref2.
Separation and characterization of this activity in WB, PRBCs and platelet
concentrates demonstrated that this activity consisted of a mixture of
lysophosphatidylcholines (lyso-PCs)ref1,
ref2.
These compounds effectively prime the PMN oxidative burst and can activate
primed adherent PMNs both in vitroref1,
ref2,
ref3,
ref4.
In addition an in vitro model of TRALI that employed human pulmonary
microvascular endothelial cells (HMVECs) as targets demonstrated that two
events were required for PMN cytotoxicityref.
The first was HMVEC activation, which demonstrated PMN adherence to the
HMVEC surface that required chemokines for PMN attraction and firm adherence
via the PMN ß2-integrins and the ICAM-1 on HMVECsref.
The second event, introduction of lyso-PCs from stored blood, could then
activate these PMNs, causing HMVEC death, and this PMN cytotoxicity could
be abrogated by inhibitors of the respiratory burstref.
-
the 2-event model of TRALI has been verified in an animal modelref1,
ref2.
Rats were treated with LPS for 2 hours to approximate active infection,
one of the predisposing clinical conditions associated with TRALIref1,
ref2.
LPS activated the pulmonary vascular endothelium resulting in pulmonary
sequestration of PMNs, which was confirmed by the pulmonary histologyref1,
ref2.
The lungs were then isolated and perfused with buffer controls or 5% heat-treated
plasma from fresh (day 0) or stored (day 5 or day 42) plasma from platelet
concentrates (apheresis platelet concentrates [A-PLTs] or whole blood–derived
platelet concentrates [WB-PLTs]) or PRBCs, respectivelyref1,
ref2.
The plasma fraction of PRBCs and platelet concentrates were taken from
the same units so that the only variable among the different plasma fractions
was storage timeref1,
ref2.
The lungs isolated from buffer pretreated animals did not evidence ALI
with any of the perfusatesref1,
ref2.
In addition, the lungs from LPS-treated animals perfused with fresh (day
0) blood components also did not evidence acute lung injury. However, lungs
from LPS pretreated animals, perfused with plasma from stored components
(day 42 PRBCs or day 5 platelet concentrates) caused ALI as documented
by pulmonary edema, lung histology, and increased leukotriene concentrations
in the perfusateref1,
ref2.
In addition, both the lipid fraction and purified lipids from stored, but
not fresh, PRBCs, WB-PLTs, and A-PLTs caused TRALIref1,
ref2.
Thus, both the plasma and lipids from stored blood products caused TRALI
in this modelref1,
ref2.
Apparently healthy patients who experience TRALI would seem to disprove
the 2-event model. However, by definition, patients who require transfusion
are not healthy. Moreover, a study of the appearance and activity of PMNs
from "healthy" donors indicated that the donors were in fact not well;
all evidenced infections, 2 with sinusitis and 3 with viral syndromes,
over the next 24 hoursref.
Thus, it may be difficult to determine if transfused patients are indeed
healthy. It is notable that TRALI has occurred, albeit rarely, in neutropenic
patients. Hypotheses regarding these reactions have included the infusion
of permeability factors including VEGF or class II HLA antibodies that
may recognize antigens on pulmonary ECs and cause EC fenestrationref
(Boshkov LK, Maloney J, Bieber S, Silliman CC. Two cases of TRALI from
the same platelet unit: implications for pathophysiology and the role of
PMNs and VEGF [abstract]. Blood. 2000;96:655a)
-
a retrospective clinical study of TRALI patients demonstrated that there
was an effective PMN priming activity, which was a lipid, in the patients’
plasma at the time that TRALI was recognized, which was not in the patient’s
pre-transfusion typing serum, and postulated that the clinical condition
of the patient was important as a first eventref.
In this study, patients with uncomplicated febrile and urticarial reactions
comprised a control group that did not demonstrate PMN priming activity
in their post-reaction blood samplesref.
Importantly, 2 of the predisposing conditions postulated by this study
to be involved with the 2-event pathogenesis of TRALI, massive transfusion
and recent major surgery, have since been implicated by other groups as
predisposing conditions for TRALIref1,
ref2,
ref3.
In a prospective analysis of TRALI, the role of cytotoxic HLA class I,
class II and anti-granulocyte antibodies were examinedref.
Of the donors tested, only 1/28 exhibited an antibody with specificity
(HLA A26) similar to positive controlsref.
The implicated blood products demonstrated significant plasma PMN priming
activity as compared to similar products from the same facility and identical
storage time that did not cause transfusion reactionsref.
There was lipid priming activity in all TRALI patients at the time of recognition,
which consisted of two classes of lipids: neutral lipids and lyso-PCsref.
In addition, the roles of IL-6 and IL-8 were examined and both increased
during storage, but only IL-6 was significantly increased in the TRALI
patients versus the pre-transfusion sampleref.
Thus, in this series TRALI was due to two events: the first was the clinical
condition of the patient, and the second was the infusion of bioactive
lipids in the stored blood componentref
Symptoms & signs : while TRALI can occur
within
6 hours of transfusion, the majority of cases present either during
the transfusion or within the first 1–2 hours
ref1,
ref2,
ref3.
TRALI is clinically identical to
ARDS
with the insidious onset of acute pulmonary distress temporally related
to transfusion
ref1,
ref2,
ref3.
The clinical findings of TRALI consist of the rapid onset of tachypnea,
cyanosis, dyspnea and fever (>= 1°C)
ref
(Popovsky MA. Transfusion related acute lung injury. In: Popovsky MA, ed.
Transfusion Reactions. Bethesda, MD: AABB Press; 2001). Auscultation of
the lungs reveals diffuse crackles and decreased breath sounds, especially
in dependent areas
ref
(Popovsky MA. Transfusion related acute lung injury. In: Popovsky MA, ed.
Transfusion Reactions. Bethesda, MD: AABB Press; 2001). The physiologic
findings include acute hypoxemia, with PaO
2/FiO
2
< 300 mm Hg, and decreased pulmonary compliance despite normal cardiac
function
ref1,
ref2,
ref3
(Popovsky MA. Transfusion related acute lung injury. In: Popovsky MA, ed.
Transfusion Reactions. Bethesda, MD: AABB Press; 2001). Radiographic examination
reveals diffuse, fluffy infiltrates consistent with pulmonary edema
ref
(Popovsky MA. Transfusion related acute lung injury. In: Popovsky MA, ed.
Transfusion Reactions. Bethesda, MD: AABB Press; 2001)
Laboratory examinations
: clinical criteria for the diagnosis of ALI and TRALI
ref
:
-
insidious, acute onset of pulmonary insufficiency
-
profound hypoxemia PaO2/FiO2 < 300 mmHg (for patients
without an arterial blood gas, pulse oximetry less than 90% meets the criteria
for hypoxemia)
-
chest radiograph:
-
bilateral fluffy infiltrates consistent with pulmonary edema
-
cardiac:
-
pulmonary artery wedge pressure <= 18 mmHg (irrespective of the pulmonary
end expiratory pressure (PEEP))
-
no clinical evidence of left
atrial hypertension

Risk factors for ALI should not exclude TRALI, for it is a form of ALI
that has a two-event etiology, with the second event related to factors
present within the transfused component(s). Moreover, worsening pulmonary
function following transfusion in a patient with compromised respiratory
status should also be considered TRALI. Patients who are transfused are
not healthy; even though patients who appear healthy may have the early
stages of an acute illness whose presentation is sub-clinical. As stated
previously, it is often difficult to assess patients who may have early
phases of acute infection
ref
Prognosis : the mortality
from TRALI is 5–25%, with lower rates being more common
ref1,
ref2,
ref3
(Popovsky MA. Transfusion related acute lung injury. In: Popovsky MA, ed.
Transfusion Reactions. Bethesda, MD: AABB Press; 2001). Most patients recover
within 72 hours; however, the data regarding TRALI are limited, and its
attendant morbidity and mortality may be underappreciated due to lack of
recognition and underreporting
ref1,
ref2,
ref3
(Popovsky MA. Transfusion related acute lung injury. In: Popovsky MA, ed.
Transfusion Reactions. Bethesda, MD: AABB Press; 2001). In addition, in
epidemiological studies of ARDS, blood transfusion was implicated as the
most common risk factor for the genesis of ARDS, and a number of these
cases may represent severe cases of TRALI
ref