1 Mini Review 1 2 3 4 Potential immune mechanisms associated with anemia in Plasmodium vivax ...

48 Pages·2014·1.35 MB·English

IAI Accepts, published online ahead of print on 4 August 2014
Infect. Immun. doi:10.1128/IAI.01972-14
Copyright © 2014, American Society for Microbiology. All Rights Reserved.
1

1 Mini Review
2
3
4
5 Potential immune mechanisms associated with anemia in Plasmodium vivax malaria:
6 a puzzling question
DDD
7 ooo
www
nnn
8 lololo
aaa
ddd
eee
ddd
9 Thiago Castro-Gomesa, Luiza C. Mourãoa, Gisely C. Melob,c, Wuelton M. Monteirob,c, fr fr fr
ooo
mmm
10 Marcus V. G. Lacerdab,c, Érika M. Bragaa h h h
ttt
ttt
ppp
:::
///
///
iaiaia
11 i.i.i.
aaa
sss
12 mmm
...
ooo
rrr
13 Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazila; g/g/g/

ooo
nnn
14 Universidade do Estado do Amazonas, Manaus, Amazonas, Brazilb; J J J
aaa
nnn
15 Fundação de Medicina Tropical Dr. Heitor Vieira Dourado, Manaus, Amazonas, Brazilc uauaua
rrr
yyy

16 303030
17 , , ,
222
18 000
111
19 888

bbb
yyy

20 ggg
uuu
eee
sss
21 ttt
22 Address correspondence to Érika M. Braga, [email protected] and
23 Marcus V.G. Lacerda, [email protected]
24
25
2

26 ABSTRACT
27
28 The pathogenesis of malaria is complex, generating a broad spectrum of clinical
29 manifestations. One of the major complications and concerns in malaria is anemia, which
30 is responsible for considerable morbidity in the developing world especially in children D
o
w
31 and pregnant women. Despite its enormous health importance, the immunological n
lo
a
32 mechanisms involved in malaria-induced anemia still remains incompletely d
e
d

33 understood. Plasmodium vivax, one of the causative agents of human malaria, is known fr
o
m

34 to induce a strong inflammatory response with a robust production of immune effectors, h
t
t
p
:
35 including cytokines and antibodies. Therefore, it is possible that the extent of the //
ia
i.
a
36 immune response may facilitate not only the parasite killing but may also provoke severe s
m
.
o
37 illness including anemia. In this review we consider potential immune effectors and their r
g
/

o
38 possible involvement in generating this clinical outcome during P. vivax infections. n

J
a
n
u
39 a
r
y

3
0
,

2
0
1
8

b
y

g
u
e
s
t
3

40
41 Malaria remains one of the most important public health problems in the world, with
42 about 3 billion people at risk of contracting the disease and 781,000 deaths estimated
43 annually (1). The global burden of human malaria is caused almost exclusively by two
44 species of parasites: Plasmodium falciparum and Plasmodium vivax. Existing research
D
45 efforts have largely focused on P. falciparum because of the higher mortality it causes, o
w
n
46 especially in Africa (2, 3). However, P. vivax remains more widely distributed than P. lo
a
d
47 falciparum and is a major public health threat affecting populous regions in Asia, horn of e
d

f
r
o
48 Africa and Central and South America (4). The spectrum of vivax malaria ranges from a m

h
49 relatively benign disease to severe and sometimes fatal illness, mainly in children (5, 6) tt
p
:
/
/
50 and pregnant women (7). The mortality rates among patients presenting P. vivax malaria ia
i.
a
s
51 is comparable to that attributable to P. falciparum malaria as evidenced by hospital-based m
.
o
r
52 studies (6, 8, 9). It has been demonstrated that chloroquine resistance parallels severe g
/

o
n
53 disease (especially severe anemia) in some areas (10). In addition to the concerns J
a
n
u
54 imposed by increasingly drug-resistant parasites, it should not be forgotten that P. vivax a
r
y

55 transmission is harder to control and eliminate than P. falciparum because the former 3
0
,

2
56 species may cause relapse after resolution of the primary infection and also due to its 0
1
8

57 early gametocytogenesis. In endemic areas, relapse of vivax malaria is an important b
y

g
u
58 source of parasite transmission to susceptible vectors and a major cause of malaria in e
s
t
59 young children (11).
60
61 BURDEN OF ANEMIA RELATED TO VIVAX MALARIA
62
4

63 In times of renewed efforts to eradicate malaria, the focus on P. vivax increases
64 considering that infections related to this species are also able to cause severe disease,
65 which includes anemia as one of the major complications (5, 12-13). Despite the striking
66 statistics, there are few studies focusing on anemia triggered by P. vivax (5, 6, 14) and
67 most of what is known about that refers to evidence obtained from studies conducted with
D
68 P. falciparum, leading to the use of proxy pathophysiological processes to explain vivax o
w
n
69 anemia. lo
a
d
e
70 Estimates of severe anemia in vivax malaria range from 1.4 to 32% (15-18). In terms of d

f
r
o
71 frequency and severity, the literature points to a greater burden of anemia particularly in m

h
t
72 young children (9, 15, 19-24) and during pregnancy (7, 25). Cross-sectional studies tp
:
/
/
73 carried out in the Brazilian Amazon, where P. vivax predominates, showed frequencies of ia
i.
a
s
74 anemia as high as 80% in children and adolescents (15, 16, 18, 19). P. vivax disease m
.
o
r
g
75 affects only 25% of children from 0-14 years old. Moreover, severe anemia was reported /

o
n
76 in hospitalized children and adults in need of red blood cell (RBC) transfusions (26). J
a
n
u
77 Severe anemia in pregnancy is an obstetric emergency in falciparum and vivax malaria- a
r
y

3
78 endemic regions (26-28). In areas of concomitant circulation of both species, the relative 0
,

2
79 frequency of vivax malaria in pregnant women ranges from 30% in Southeast Asia (18, 0
1
8

b
80 25, 29) to nearly 80% in Latin America (30-32), pointing to an increasing risk of anemia y

g
u
81 in this latter region. Severe neonatal anemia was also reported in a study conducted in e
s
t
82 Colombia (33). Indeed, an extensive data evaluation from hospitalized newborns in the
83 Indonesian Papua revealed that severe anemia has an important clinical impact in young
84 infants with congenital malaria (18).
85
5

86 OVERVIEW OF THE MAJOR DETERMINANTS OF VIVAX ANEMIA
87
88 Malaria is an intravascular infection that results essentially from the presence of blood
89 stage parasites inside RBCs during its intra-erythrocytic cycle. Hematological
90 disturbances, therefore, may be caused by the destruction of RBCs, the release of
D
91 parasites and RBC debris into the circulation, and finally, due to a host reaction to these o
w
n
92 events (34). Although several mechanisms are likely to participate in the generation of lo
a
d
e
93 anemia in individuals infected with malarial parasites, they may be grouped into two d

f
r
o
94 main categories: (i) destruction of RBCs in the peripheral circulation, spleen and bone m

h
t
95 marrow and (ii) dyserythropoiesis (Figure 1). tp
:
/
/
96 Since P. vivax merozoites prefer reticulocytes as host cells (35), as opposed to P. ia
i.
a
s
97 falciparum, which targets all types of RBCs, the density of peripheral parasitemia in m
.
o
r
g
98 vivax malaria is often lower than that detected in falciparum infections (36). Despite of /

o
n
99 this, studies on antimalarial therapy have demonstrated that P. vivax is responsible for a J
a
n
u
100 comparable decrease in the RBC mass since it results in a four-fold higher removal of a
r
y

3
101 non-infected RBCs when compared to P. falciparum (37, 38), and in part due to the fact 0
,

2
102 that the invasion of reticulocytes interferes with the supply of mature RBCs (37, 39-41). 0
1
8

b
103 In P. falciparum infection 8.5 uninfected RBCs per infected RBC are destroyed (38, 42), y

g
u
104 while in P. vivax infection, this number is estimated to be around 34 RBCs (37). A P. e
s
t
105 vivax-infected reticulocyte is up to two times larger than a non-infected RBC and
106 Schüffner's dots associated with caveolae-vesicle complexes are seen along the infected
107 RBC plasmalemma (43, 44). Contrary to P. falciparum, RBC deformability seems to be
108 increased in P. vivax infection (45, 46). As a consequence, P. vivax-infected RBCs
6

109 decrease their clearance during their passage through the spleen sinusoids, making
110 sequestration and obstruction to blood flow unlikely in vivax malaria (47).
111 Another important contributor to anemia is the reduced deformability of non-parasitized
112 RBCs, as experimentally demonstrated in falciparum malaria. At high shear stresses,
113 erythrocytes increased their rigidity and were removed in the spleen (48). In relation to
D
114 vivax malaria, it has been demonstrated that after passage under microfluidic conditions o
w
n
115 simulating splenic filter and fine capillary beds, about 15% of non-parasitized RBCs were lo
a
d
e
116 lost (46). This observation suggests another possible mechanism for RBC destruction, d

f
r
o
117 although how it occurs is still unknown. m

h
t
118 Other features of P. vivax parasites that could be associated with the pathogenesis of tp
:
/
/
119 severe anemia are rosetting (49, 50) and cytoadherence, a phenomenon that has been ia
i.
a
s
120 recently described in vivax malaria (51-54). In vitro studies showed that P. vivax infected m
.
o
r
g
121 RBCs are able to cytoadhere to endothelial cells from the human lung (54) and also to /

o
n
122 human placental microvasculature (51, 53). It has also been suggested that in the human J
a
n
u
123 spleen, P. vivax attaches to barrier cells to avoid its clearance from circulation, allowing a
r
y

3
124 the release of merozoites in a reticulocyte-rich environment (55, 56). Nevertheless, how 0
,

2
125 cytoadherence influences anemia associated with vivax malaria remains to be 0
1
8

b
126 investigated. In relation to rosetting, this phenomenon was verified in vitro for cells y

g
u
127 containing parasites with visible malaria pigment (49), and it has been considered a e
s
t
128 potential contributor to the hypothesized but uncharacterized microvascular obstruction
129 and end-organ pathology described in vivax malaria (57). Recently, another route of
130 normal RBC removal was proposed in a study conducted with Kenyan children
131 presenting natural P. falciparum infection. According to this work 4-hydroxynonenal, a
7

132 biomembrane lipid peroxidation product, is prone to diffuse in the rosettes, from P.
133 falciparum parasitized RBCs to the non-parasitized ones, leading to their clearance by
134 macrophages (58). Notwithstanding, it is unknown whether this process also occurs in P.
135 vivax infection.
136 It is noteworthy that the overall inflammatory response seems to be stronger in vivax than
D
137 in falciparum malaria (59, 60), and it is possible that the modifications in non-infected o
w
n
138 RBCs surface may be a direct consequence of cytokine imbalance (61) and oxidative lo
a
d
e
139 damage (62). d

f
r
o
140 P. vivax infection is accompanied by changes in the host antioxidant defense system, m

h
t
141 which reverses after chloroquine treatment (63). The increase in reactive oxygen species tp
:
/
/
142 (ROSs) may deplete RBCs defense mechanisms, comprising particular intracellular ia
i.
a
s
143 enzymes, e.g. superoxide dismutase, catalase, and the glutathione system (64, 65). In this m
.
o
r
g
144 manner, alterations in the redox status would play an important role in the pathogenesis /

o
n
145 of disease, including anemia, as it has been proposed for P. falciparum (66). J
a
n
u
a
r
146 As host genetic factors may exert some influence on malaria susceptibility, these y

3
0
147 parameters should be considered as important determinants of the anemia onset. ,
2
0
1
148 However, few studies have focused on investigation about human genetic variants that 8

b
y

149 confer some degree of protection/resistance against P. vivax and anemia, limiting our g
u
e
s
150 understanding about the associations between these polymorphims and infection (67). It t
151 is well established that P. vivax endemicity and estimates of populations at risk are
152 strongly influenced by proportion of the Duffy antigen-negative individuals relatively
153 refractory to the P. vivax infection (4, 68). FY*B/FY*X and FY*A/FY*X genotypes are
154 associated with low parasite density, which may favorably impact hemoglobin levels
8

155 (69). Observational studies have shown a protection against P. vivax infections conferred
156 by a RBC enzyme deficiency (glucose-6-phosphate dehydrogenase deficiency) (70-72)
157 and an erythrocyte membrane disorder (Southeast Asian ovalocytosis) by a mechanism
158 that is independent of the Duffy antigen (73). On the other hand, thalassaemias, disorders
159 of globins synthesis, appear to increase the susceptibility to vivax malaria in carrier
D
160 populations from different geographic regions (74-77). The reasons why individuals with o
w
n
161 thalassaemias may be more prone to malaria are related to their ineffective erythropoiesis lo
a
d
e
162 as well as their shortened RBC survival, which leads to a high cell turnover, increasing d

f
r
o
163 their reticulocyte counts, and favoring the infection of these cells by P. vivax (76-78). m

h
t
164 Interestingly, a different association was observed in falciparum malaria, in which tp
:
/
/
165 thalassaemia would decrease the susceptibility to P. falciparum, confering protection ia
i.
a
s
166 against severe disease such as anemia (79). This protection appears to be related to the m
.
o
r
g
167 higher levels of antibodies that bind to parasitized erythrocytes (80), allowing their /

o
n
168 phagocytosis by blood monocytes (81). J
a
n
u
a
r
169 y

3
0
,

2
170 DYSERYTHROPOIESIS AND IMMUNE-MEDIATED ANEMIA 0
1
8

b
y

171 During a plasmodial infection, the normal erythropoiesis is disturbed in patients with g
u
e
s
172 malaria, reflecting an erythropoietic suppression and subsequent dyserythropoiesis. In the t
173 acute phase of malaria, the ineffectiveness of erythropoiesis may be evidenced by the
174 presence of normal or reduced cellularity associated with a reduced percentage of
175 erythroblasts. On the other hand, in the chronic phase, it may be deduced by an increase
176 in marrow cellularity and also in erythroblast percentage (82).
9

177 A series of studies performed with both P. falciparum and P. vivax infections have shown
178 that a common feature in anemic patients with malaria is the presence of defective
179 erythroblasts exhibiting various abnormalities such as cytoplasmatic vacuolation, nuclei
180 with irregular shape or multinuclearity, intercytoplasmatic bridges and loss or
181 myelinisation of parts of nuclear membrane, among others (82-85). These studies have
D
182 also demonstrated the presence of erythroblasts in different stages of degradation inside o
w
n
183 the cytoplasm of macrophages from bone marrow, suggesting that erythrophagocytosis lo
a
d
e
184 was an important mechanism involved in the degradation of injured erythroblasts (86). d

f
r
o
m
185 Data obtained by transmission electron microscopy revealed two cases of vivax malaria h
t
t
p
:
186 in which parasites were detected in erythroblasts, suggesting that the destruction of these /
/
ia
i.
187 cells by P. vivax could be an underlying mechanism contributing to P. vivax-related a
s
m
.
188 anemia (87). Moreover, bone marrow aspirate from a Brazilian Amazon patient with o
r
g
/

o
189 chronic P. vivax infection presenting with splenomegaly and thrombocytopenia showed n

J
a
190 schizonts inside RBCs, without parallel detection of parasites in the peripheral blood n
u
a
r
191 (88). y

3
0
,

2
192 Recently, an in vitro study conducted with hematopoietic CD34+ cells derived from 0
1
8

b
193 umbilical cord blood showed that P. vivax could inhibit erythroid development directly. y

g
u
194 The authors also showed that the presence of the parasite inhibited the growth as well as e
s
t
195 the differentiation of the erythroid progenitors (41). However, despite the fact that the
196 parasite has perturbed cell division and differentiation, it did not lead to cell death.
197 Therefore, the importance of erythroblast parasitism in severe P. vivax anemia is still
10

198 elusive and unlikely the situation that occurs in P. falciparum infection, in which there is
199 obstruction of the bone marrow microvasculature by parasitized red blood cells (86).
200 Besides the parasite direct effects, the defective erythropoiesis in malaria may also be
201 linked to parasite-derived molecules that cause a toxic effect in erythroblasts or in other
202 erythroid progenitor cells. A second possibility that may also exert influence in
D
o
w
203 erythropoiesis is the production of immune mediators, by host cells, as a response to
n
lo
a
204 parasite products; when released, these mediators would damage surrounding d
e
d

205 haematopoietic cells, altering their morphology and function (82). In this direction, it has fr
o
m
206 been demonstrated that the presence of hemozoin, a metabolic product generated during h
t
t
p
:
207 the digestion of hemoglobin, in plasma, leukocytes, or in erytroid precursors, was able to /
/
ia
i.
208 inhibit erythropoiesis (89). Studies conducted with bone marrow sections obtained from a
s
m
.
209 children who died as a result of severe malaria showed an association between the o
r
g
/

o
210 amount of hemozoin and the proportion of abnormal erythroid cells (90). The negative n

J
a
211 effects of hemozoin in the erythroid expansion seem to be related to its ability to n
u
a
r
212 stimulate the release of cytokines, chemokines or lipo-peroxidases, molecules that inhibit y

3
0
213 erythropoiesis by bone marrow macrophages (90). Although hemozoin has been ,
2
0
1
214 considered as an important mediator of apoptosis leading to impairment in RBC 8

b
y

215 production during falciparum anemia (90), it remains unknown whether a similar g
u
e
s
216 phenomenon also occurs during P. vivax infections. t
217 An imbalance in the production of host immune mediators could be another important
218 factor contributing to anemia, especially in P. vivax malaria, in which the inflammatory
219 response seems to be more intense than that observed in P. falciparum infections with a
220 similar parasite biomass (59, 60, 91, 92). It has been shown that P. vivax patients