Capillaria hepatica
-induced hepatic fibr osis in r ats:
par adoxical effect of r epeated infections
Fibrose do fígado e
Ca pilla ria he pa tica
em ratos:
efeito paradoxal nas infecções repetidas
Ludmila Oliveir a1, Már cia Mar ia de So uza2 and Zilto n A. Andr ade3
ABSTRACT
Mu lti p le e x p o su re s to p a ra si ti c a ge n ts a re c o n si d e re d a n i m p o rta n t f a c to r i n th e ge n e si s o f th e m o st se ve re f o rm s o f th e d i se a se s th e y c a u se . Capillar ia he patic a- i n d u c e d se p ta l f i b ro si s o f th e li ve r i n ra ts u su a lly ru n s wi th o u t si gn s o f p o rta l hype rte n si o n o r he pa ti c f a i lu re . Af te r de te rm i n i n g the he pa ti c pro f i le o f 15 a n i m a ls du ri n g the c o u rse o f a si n gle i n f e c ti o n , we su b m i tte d 2 0 ra ts to m u lti p le Capillar ia he patic a i n f e c ti o n s to d e te rm i n e wh e th e r re p e a te d e x p o su re s wo u ld a u gm e n t f i b ro si s pro du c ti o n , tra n sf o rm i n g se pta l he pa ti c f i b ro si s i n to a tru e c i rrho si s. Te n si n gle - i n f e c ti o n ra ts se rve d a s c o n tro ls. A to ta l o f 5 e x p o su re s, wi th 4 5 - d a y i n te rva ls, we re m a d e . Hi sto lo gi c a l c h a n ge s we re f o llo we d b y m e a n s o f su rgi c a l li ve r b i o psi e s, c o lle c te d pri o r to i n f e c ti o n a n d to e a c h re - i n f e c ti o n . Fu n c ti o n a l c ha n ge s we re m i n i m a l a n d tra n si e n t. Altho u gh a sli gh t re c ru d e sc e n c e o f f i b ro si s wa s o b se rve d a f te r th e f i rst two re - i n f e c ti o n s a n d wh e n th e si n gle - i n f e c te d c o n tro l gro u p wa s re - i n f e c te d a t th e e n d o f th e e x p e ri m e n t, su b se q u e n t re - i n f e c ti o n s f a i le d to i n c re a se th e a m o u n t o f f i b ro si s. On th e c o n tra ry, th e re o c c u rre d q u a n ti ta ti ve a n d q u a li ta ti ve e vi d e n c e o f c o lla ge n d e gra d a ti o n a n d su p p re ssi o n o f p a ra si te d e ve lo p m e n t. Th e se p a ra d o x i c a l re su lts a re i n k e e p i n g wi th th e h yp o th e si s th a t a c o m p le x i m m u n o lo gi c a l m o d u la ti o n p a rti c i p a te s i n th e m e c h a n i sm o f h e p a ti c f i b ro si s i n d u c e d b y Capillar ia he patic a i n f e c ti o n i n ra ts.
Ke y-wor ds:Capillar ia hepatic a. He pa ti c f i b ro si s. Re pe a te d i n f e c ti o n s.
RESUMO
As in fe c ç õ e s re pe tida s sã o c o n side ra da s u m im po rta n te fa to r n a pa to ge n ia da s fo rm a s m a is gra ve s da s do e n ç a s c a u sa da s po r pa ra sito s. A fib ro se da he pa to pa tia c a u sa da po r Capillaria hepatic a e m ra to s c u rsa n a a u sê n c ia de sin a is de hipe rte n sã o po rta o u insuficiê ncia he pá tica . De po is de de te rm ina r o pe rfil he pá tico e m 15 a nim a is dura nte o curso de um a infe cçã o , sub m e te m o s 20 o u tro s ra to s a in fe c ç õ e s re pe tida s, n u m a te n ta tiva pa ra pro du zir fo rm a s m a is gra ve s, c o m e xc e sso de fib ro se e e vo lu ç ã o pa ra a c irro se . Ao to do fo ra m fe ita s c in c o in fe c ç õ e s, c o m in te rva lo de 45 dia s e n tre a s m e sm a s. As a lte ra ç õ e s fo ra m se gu ida s a tra vé s b ió psia s he pá tic a s to m a da s a n te s da in fe c ç ã o e de c a da re - in fe c ç ã o . Um gru po c o n tro le , c o m in fe c ç ã o sim ple s fo i u sa do pa ra c o m pa ra ç ã o . As a lte ra ç õ e s fu n c io n a is fo ra m m ín im a s e tra n sitó ria s. Em b o ra te n ha sido n o ta do u m lige iro a u m e n to da fib ro se n a 2a e 3a re - in fe c ç õ e s o u q u a n do o gru po c o n tro le fo i re - in fe c ta do a o té rm in o do e xpe rim e n to , a s
in fe c ç õ e s re pe tida s n ã o c a u sa ra m a u m e n to da fib ro se . Pe lo c o n trá rio , fo ra m o b se rva do s sin a is de de gra da ç ã o da fib ro se e de inte rfe rê ncia co m o de se nvo lvim e nto pa ra sitá rio . Este s re sulta do s pa ra do xa is a pó ia m a suge stã o de que um co m ple xo m e ca nism o de m o du la ç ã o im u n o ló gic a e stá e n vo lvido n a pro du ç ã o da fib ro se he pá tic a in du zida pe la Capillar ia hepátic a e m ra to s.
Palavr as-chave s:Capillaria hepatic a. Fi b ro se he pá ti c a . In f e c ç õ e s re pe ti da s.
1 . PIB IC Stude nt ( CNPq /UFB A) . 2 . Maste r in Patho lo gy – FIOCRUZ/UFB A. 3 . He ad, Lab o r ato r y o f Expe r ime ntal Patho lo gy, Go nç alo Mo niz Re se ar c h Ce nte r, FIOCRUZ, B ahia.
Suppo r te d b y PAPES III, Oswaldo Cr uz Fo undatio n and PIB IC ( CNPq /UFB A) .
Addr e ss to: Dr. Zilto n A. Andr ade . Ce ntr o de Pe sq uisas Go nç alo Mo niz/FIOCRUZ. Rua Valde mar Falc ão 1 2 1 , 4 0 2 9 5 - 0 0 1 Salvado r, B A, B r azil. e - mail: zilto n@ c pq gm. fio c r uz. b r
Re c e b ido par a pub lic aç ão e m 2 8 /1 1 /2 0 0 3 Ac e ito e m 1 3 /2 /2 0 0 4
Septal fibrosis of the liver regularly appears in rats infec ted with the he lminth Ca p i lla ri a h e p a ti c a8. The wo r ms matur e
exc lusively inside the liver and die and disintegr ate so o n after e gg la ying in r a ts. This o c c ur s b y the 2 0th- 2 5th da y a fte r
and reso rptio n8 1 6. Altho ugh the dead-wo rm lesio ns tend to
disappear, septal fibrosis seems progressive, at least during the first two-three months after infection8. Soon its fine and long fibrous
septa involve the whole liver parenchyma, connecting portal space to portal spac e, and eventually to c entral veins, c reating a mosaic pattern of pseudo-lobules that resembles secondary biliary cirrhosis. However, this morphologic al pic ture is assoc iated neither with signs o f pr o gr e ssive dise a se no r with e vide nc e o f po r ta l hypertension or hepatic failure. Indeed the functional counterpart of the C. he pa tica model needs to be better investigated.
Shibayama and Nakata1 5 demonstrated that rats with septal
hepatic fibrosis induc ed by repeated intraperitoneal injec tions of pig serum presented portal pressure, oxygen c onsumption and liver weight c omparable to normal c ontrols. They c onc luded that the simple presenc e of hepatic fibrosis does not nec essarily alter c ir c ulato r y dynam ic s and he pato c e llular func tio n. Altho ugh
C. he pa tic a-induc ed septal fibrosis presents similar intensity and distribution as that found in the pig-serum model, one should c onsider that in the former there are in addition the foc al lesions produc ed by dead or dying parasites, and their eggs.
The present investigation has a two-fold objec tive: to perform a pr eliminar y and gener al study o f the hepatic func tio n in c orrelation with the formation and evolution of C. he pa tic a -induc ed septal fibrosis in rats; and to determine whether multiple exposure to C. he pa tica infec tion would result in an aggravation of the lesions, and the produc tion of a true parasitic c irrhosis.
MATERIALS AND METHODS
Anima ls. Yo ung adult Wistar r ats o f b o th se xe s, we ighing 1 5 0 - 2 0 0 g, m a in ta in e d in go o d a n d c o n tr o lle d h o us in g c o nditio ns o f humidity and te mpe r atur e , with fr e e ac c e ss to wate r and to a pe lle t-b alanc e d c o mme r c ial die t we r e use d thro ugho ut the experiments.
Inoculum. Consisted of embryonated eggs of C. he pa tica
administered by means of a gastric tube. The eggs were obtained from the livers of experimentally infected mice. These organs were added to a small quantity of tap water and homogenized in an electric blender at 1 ,0 0 0 rpm/3 min, followed by washing and decantation. The clean immature eggs obtained were left in a humidified Petri dish fo r 2 8 -3 0 days, at 2 6 -2 8oC to e mb r yo nate , whe n the y we r e
c o unted in a mic ro sc o pe and used. Mo re details regarding the o b taining, pr e par atio n and c o unting o f the ino c ulum ar e de sc r ib e d e lse whe r e8 1 0 1 6. The amount of eggs in the inoculum
varied in different experiments, but that has been demonstrated not to interfere with the results as far as septal fibrosis is concerned 1 2.
De te r mina tio n o f the he pa tic functio na l pr o file . A group of 1 5 rats were infec ted with 6 0 0 embryonated C. he pa tica
eggs. Tail vein blood was c ollec ted from all animals. Sera taken fro m pre-infec ted animals ( Co ntro ls) and 4 3 and 7 6 days after i n fe c ti o n we r e s u b m i tte d to b i o c h e m i c a l a n a l ys i s fo r aminotransferases ( ALT and AST) , alkaline phosphatase, gamma-glutamyl-transpeptidase ( G-GT) , total and direc t bilirubin, and alb umin b y me ans o f an auto matic analyze r Hitac hi 9 1 7 at the B ahia State Central Labo rato ry ( LACEN) .
Re pe a te d infe ctio ns. Twe nty animals we r e sub mitte d to five infe c tio ns, e ac h with 1 0 0 e mb r yo nate d e ggs at 4 5 -day inte r vals, to taling o ne infe c tio n and fo ur r e -infe c tio ns. At the time the animals we r e b e ing sub mitte d to the 5th infe c tio n, it
was de c ide d that the r e maining 3 animals fr o m the 1st Gr o up
( single -infe c tio n c o ntr o ls) , sho uld also b e r e -infe c te d, sinc e the ir r e spo nse , afte r a pr o lo nge d inte r val fr o m fir st infe c tio n, appear ed to b e o f inter est.
Single - infe c tio n. Te n anim als we r e sub m itte d to an infec tio n with 1 0 0 embryo nated C. he pa tic a eggs and rec eived no fur the r ino c ula tio n, the s e we r e fo llo we d in a ll o the r pr o c edur es as c o ntr o ls.
Specimens collected. Fragments of the liver were c ollec ted by surgic al biopsy from all animals at 4 5 days from the last inoc ulation. In addition, one animal from the single-infec tion group and three from the repeated-infection group were sacrificed at eac h experimental period. The liver fragments obtained either b y b io psy o r auto psy we r e fixe d in 1 0 % ne utr al fo r malin, embedded in paraffin and the bloc ks c ut in a mic rotome at 5 -1 0 mic rometers. The sec tions were stained with hematoxylin and eosin, and with the Sirius-red method for c ollagen.
Evaluation of fibr osis. 1 . Hydro xypro line de te rm ina tio n: bioc hemic al determination of hydroxyproline c ontent was made ac c ording to the c olorimetric method of B ergman & Loxley2.
2 . S e m i q u a n ti ta ti ve a n a l ys i s : fi b r o s i s wa s s e m i -q ua n tita tive ly e va lua te d un de r th e m ic r o s c o p e , b y two inde pe nde nt o b se r ve r s unawar e o f the r e spe c tive pr o to c o ls, from Sirius-red stained slides as minimal ( + ) , moderate ( + + ) and marked ( + + + ) . These degrees represented, respec tively: ( + ) whe the r se ptal fib r o sis appe ar e d in a fe w fo c al ar e as, usually at the pro ximity o f parasitic lesio ns, leaving mo st o f the l i ve r p a r e n c h ym a u n i n vo l ve d; ( + + ) fi b r o s i s o b s e r ve d thro ugho ut the liver, but with very thin septa, largely separated o ne fr o m the o the r, and so me o f the m inc o mple te ; ( + + + ) pr o minent and lar ger septa, tho r o ughly distr ib uted within the liver. No c ase o f absenc e o f fibro sis was fo und in any examined sec tion.
Se r um a ntibo die s. Se r a we r e c o lle c te d at sac r ific e and sub mitte d to an ELISA te st fo r de te c tio n o f to tal Ig anti-C. he pa ti c a antibo dies, by using a go at anti-rat IgG c o nj ugated to pe r o xida se ( Sigm a , Sa int Lo uis, MO, USA) . The pla te s we r e s e n s itize d with 1 0
µ
g/m l/pe r we ll o f C. h e p a ti c a- e gg a n d wo r m a n tige n , dilute d in c a r b o n a te b uffe r, pH 9 . 6 Re a din g wa s do n e us in g a m ic r o pla te r e a de r Mo le c u la r d e vi c e s-Th e rm o m a x spe c tr o pho to me te r ( Sunyvale y, CA, USA) unde r wave le ngth 4 5 0 nm , c o nne c te d to a c o m pute r r unning MDS-So ft Max.Statistical analysis. The numeric al analysis o f the serum antib o dy le ve ls o b taine d b y the ELISA te st, and tho se de r ive d fr o m the b io c he mic al me asur e me nts o f hydr o xypr o line was made by the Student-Newman-Keuls o ne-way-ANOVA.
RESULTS
infec tion did not c ause muc h deviation from normal, exc ept for a slight inc rease in alkaline phosphatase and aminotransferase le ve ls dur ing the 4 5th day o f infe c tio n, a mo me nt whe n fo c al
nec ro -inflammato ry parasitic lesio ns are pro minent.
Quantitative data o n fib r o sis, as r evealed b y measur ement o f hydr o xypr o line c o nte nt, ar e pr e se nte d in Figur e 1 . The y revealed that repeated infec tion with C. he pa tic a did not result in signific ant inc r e ase o f live r fib r o sis. The r e was a slight inc rease following a sec ond infec tion, espec ially when animals with long-duration single infec tion ( c ontrols) were re-infec ted
The liver s o f all the animals, mic r o sc o pic ally examined o n the 4 5th day o f infe c tio n, sho we d a unifo r m pic tur e o f fo c al
par asite-der ived inflammato r y lesio ns and septal fibr o sis. The fo c al le sio ns we r e e nc apsulate d and c o ntaine d ne c r o tic adult worms and eggs, in and around them, mixed with a ric h c ellular exudate ( Figure 3 A) . Fibro us septa were seen aro und the fo c al par asitic le sio ns and distant fr o m the m, usually c o nne c ting po r tal spac e s to ano the r po r tal spac e . The amo unt o f fib r o sis was var iab le fr o m c ase to c ase .
Forty-five days later, these main findings c ontinued without signific ant modific ations. The parasitic lesions bec ame smaller than before; most of the central parasitic debris had been removed, leaving c lusters of parasite eggs in its plac e. Calc ific ation was present in some parasitic foc i. These lesions were similarly found both in the animals with single or two infec tions. Septal fibrosis was evident throughout the liver, and more marked in the re-infec ted animals.
Ar o und the 1 2 0th day fr o m the fir st ino c ulatio n, a no tab le
differenc e was fo und regarding the fo c al parasitic lesio ns seen in the animals sub mitte d to thr e e r e pe ate d infe c tio ns and the single-infec ted c ontrols. While the remnants of the worms almost disappe ar e d fr o m the fo c al le sio ns in the latte r, c o lle c tio ns o f live immatur e wo r ms we r e fo und in the fo r me r ( Figur e 3 B ) . So me mo r e develo ped wo r ms pr esented a few eggs, delimited Ta b le 1 – He p a ti c f u n c ti o n a l p ro f i le i n Capillar ia he pátic a- i n f e c te d ra ts.
Te st Co ntro ls I NF. 4 3 Days I NF. 7 6 Days
( N= 5 ) ( N= 5 ) ( N= 9 )
To tal Pr o te ins 6 ,7 ± 0 ,3 6 ,9 ± 0 ,3 6 ,6 ± 0 ,3
Alb umin 4 ,1 ± 0 ,2 4 ,0 ± 0 ,1 4 ,3 ± 0 ,2
TGO ( AST) 1 4 0 , 8 ± 7 ,8 1 6 2 ,2 ± 3 5 ,2 1 5 0 ,0 ± 3 2 ,2
TGP ( ALT) 6 8 ,4 ± 1 4 ,7 9 2 ,2 ± 2 2 ,4 5 8 ,0 ± 4 ,7
Ga m m a - GT 5 ,8 ± 2 ,6 4 ,2 ± 0 ,8 5 ,0 ± 0 ,3
Alk aline pho sphatase 1 3 9 ,4 ± 4 3 ,2 3 6 7 ,6 ± 5 0 ,8 1 0 9 ,8 ± 2 5 ,4
To tal b ilir ub in 0 ,3 ± 0 ,1 0 ,2 ± 0 ,1 0 ,3 ± 0 ,1
Dir e c t b ilir ub in 0 ,1 ± 0 ,1 0 ,1 ± 0 ,0 0 ,1 ± 0 ,0
at the time the o ther s wer e r ec eiving their 5th ino c ulatio n. The
se mi-quantitative analysis o f histo lo gic al pic r o -sir ius staine d slides yielded similar results. Searc h for anti-C. he pa tic a serum antib o die s r e ve ale d pr o gr e ssive ly inc r e ase d le ve ls dur ing r epeated ino c ulatio ns ( Figur e 2 ) . Single-infec ted animals that were re-infec ted later, at the time of the 5th re-infec tion, showed
a signific ant inc rease in hydroxyproline measurements, without inc r ease in ser um-antibo dy levels.
h
ip
r
o
g
/g
1 0
7 . 5
5 . 0
2 . 5
0 , 0
1st
infe c . 1nd
infe c . 1th
infe c . 1th
infe c . 1th
infe c . 1th
infe c .
Fi gu ra 1 - Hyd ro x i p ro li n e m e a su re m e n ts i n ra t li ve rs f o llo w i n g si n gle a n d re p e a te d i n f e c ti o n s w i th Capillar ia he patic a p > 0 .0 5 .
1 . 5
1 . 0
0 . 5
0 . 0
O
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ti
c
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l
d
e
n
s
it
y
C R 1 C R 2 C R 3 C R 4 C R 5 C*
* Represents c ontrol single-infec ted rats that were re-infec ted 8 mounths later.
Fi gu re 2 - An ti -Capillar ia he patic a se ru m a n ti b o d y le ve ls i n ra ts, e va lu a te d w i th 4 5 - d a ys i n te rva ls, i n si n gle - i n f e c te d a n i m a ls ( C) a n d i n su c c e ssi f u lly re - i n f e c te d o n e s ( R) . p < 0 .0 5 .
Figure 3 - A) Necro tic wo rm s surro unded by a ca psule o f m a cro pha ges m ixed with lym p h o c yte s, lo c a te d n e a r a p o rta l sp a c e , wh i c h sh o ws c o n c e n tra ti o n o f m o no nuclea r leuk o cytes a ro und a bile duct. H & E, 100X. B) A co llectio n o f live i m m a tu re w o rm s w i th i n a n e c ro - i n f la m a to ry a re a a p p e a rs i n th e li ve r pa renchym a o f a ra t, 45 da ys a fter the 3rd re-infectio n a nd 120 da ys fro m the first
by thin and transparent shells, lo c ated bo th within and aro und their bodies. Fibrous septa present in both groups bec ame very thin and frequently interrupted or fragmented, exhibiting a wavy patte r n inste ad o f the pr e vio us str aight o ne . Fr o m the n o n, these featur es j ust desc r ib ed b ec ame mo r e and mo r e evident. Fe we r and fe we r, de ad and live immatur e wo r ms appe ar e d in the fo c al le sio ns fr o m the animals sub mitte d to r e -infe c tio ns. Non-spec ific inflammatory reac tions were minimal around them. Se ptal fib r o sis b e c ame r e sidual. Invo lutive le sio ns we r e also observed in animals submitted to single infec tion. Parasite eggs appeared c onc entrated in foc al c ollec tions within the liver. Foc al lesio ns wer e atr o phic and c alc ified ( Figur e 4 ) . Septal fib r o sis was le ss and le ss e vide nt, b ut was pr e se nt as thin and lo ng septa, sometimes more evident than that observed in repeatedly infec ted animals. This regressive histologic al pic ture appeared to b e stab ilized fr o m ar o und the 4th mo nth o n ( Figur e 5 ) .
DI SCUSSI ON
Ca pi lla ri a h e p a ti c a in fe c tio n is we ll to le r a te d in r a ts . The a s s o c ia tio n with diffus e s e pta l fib r o s is do e s no t s ignify a m a j o r im p a c t o n h e p a tic fun c tio n , th e p r o file o f wh ic h c h a n ge s ve r y little dur in g th e c o ur s e o f in fe c tio n . I n th is q ue s tio n , o ur fin din gs c o n fir m th o s e o f Sh ib a ya n a a n d Na k a ta o b s e r ve d in s e pta l fib r o s is in duc e d b y pig- s e r um1 5.
R e - e x p o s ur e to in fe c tio n is s up p o s e dly a n im p o r ta n t e ve n t i n th e de ve l o p m e n t o f th e m o s t s e ve r e fo r m s o f p a r a s i ti c d i s e a s e s . T h e d e c r e a s e i n m o r ta l i ty a n d i n m o r b idity wh ic h h a s b e e n o b s e r ve d fo llo win g th e o ffic ia l c a m pa ign fo r Tri a to m a i n f e sta n s e r a dic a tio n in e n de m ic a r e a s o f Ch a ga s ’ di s e a s e , i n di r e c tl y p o i n ts to wa r d th e im po r ta n c e o f r e - e x po s ur e to in fe c tio n a s a n a ggr a va tin g fa c to r i n th e p a th o ge n e s i s o f p a r a s i ti c d i s e a s e7. T h e
i m p o r t a n c e o f r e - i n f e c t i o n i n a g g r a va t i n g t h e c lin ic o pa th o lo gic a l c o ur s e o f pa r a s itic dis e a s e s h a s b e e n de m o n s tr a te d fo r s c h is to s o m ia s is . Th e de ve lo p m e n t o f h e p a to s p le n ic dis e a s e , with its a c c o m p a n yin g p e r ip o r ta l fi b r o s i s a n d i n tr a - h e p a ti c va s c u l a r o b s tr u c ti o n r a r e l y o c c ur s in infe c te d patie nts m igr ating away fr o m an e nde m ic a r e a6. Tr a n s m is s io n c o n tr o l in a n is o la te d e n de m ic a r e a o f
th e s ta te o f B a h ia , B r a zil, wa s fo llo we d b y a m e lio r a tio n o f c linic al m anife statio ns and b y suppr e ssio n o f he pato sple nic d i s e a s e d e ve l o p m e n t4. E x p e r i m e n t a l l y, p e r i o vu l a r
gr a n u l o m a s a r e l a r ge r5 a n d p e r i p o r ta l fi b r o s i s m o r e
Figu re 4 - In vo lu tive fo c a l pa ra sitic le sio n s. To p a n d m iddle pic tu re s illu stra te th e sh ru n k e n , c a lc i f i e d a n d e n c a p su la te d f o c a l le si o n s c a u se d b y d e a d pa ra si te s a n d e ggs i n the li ve r o f ra ts, i n spi te o f re pe a te d i n f e c ti o n s wi th Capillr ia hepatic a. H & E, 200X. The pic tu re a t b o tto m sho ws in vo lu tive c ha n ge s b o th i n f o c a l pa ra si ti c le si o n a n d i n se pta l f i b ro si s pre se n t i n the li ve r o f a ra t a fte r 3 re - in fe c tio n s with Capillar ia hepatic a. Siriu s- re d fo r c o lla ge n , 100X.
Fi gu re 5 - A) se p ta l f i b ro si s o f th e li ve r i n a ra t 4 5 d a ys a f te r a f i rst i n f e c ti o n . Fi b r o u s s e p t a a p p e a r p r o m i n e n t , c o n n e c t i n g p o r t a l s p a c e s . B t o F) i llu stra te s d e gra d a ti ve c h a n ge s o f f i b ro u s se p ta a p p e a ri n g f ro m th e 4th re
fr e q u e n t i n m i c e s u b j e c te d to r e p e a te d s c h i s to s o m a l in fe c tio n s1 4. I n c ases o f intestinal helminthiasis the severity o f
the c linic al r e pe r c ussio ns is usually dir e c tly r e late d to wo r m load. Of c ourse it may be the result of a heavy primary infec tion, b ut in many c ase s multiple r e -infe c tio ns c an b e implic ate d (Asc a ris, Anc ylo sto m a, and even Tric huris) . The c yc le of auto-infe c tio n in Stro n gylo i d s ste rc o ra li s infe c tio n, b y inc r e asing the wo r m b ur de n, is the b asis o f the se ve r e st c ase s o f this he lm inthia sis o b se r ve d in m a n1. The r e fo r e , the situa tio n o f
C. h e p a ti c a o b se r ve d in the pr e se nt study mak e s a str ik ing exc eptio n. The immuno lo gy o f C. he pa ti c a infec tio n has b een little investigated, espec ially c o nc er ning the pr o b lems r elated to re-infec tio ns9 1 7. Mo st o f the c ases o bserved in humans have
b e e n c har ac te r ize d b y he avy wo r m b ur de n, pr o b ab ly due to a massive fir st infe c tio n1 3, b ut similar e ve nts have no t b e e n
desc ribed in c ases observed in natural infec tions of animals 9 1 7.
B ut, if th e da ta o n s us c e p tib ility a n d r e s is ta n c e o f r a ts to
C. he pa ti c a infe c tio n ar e fe w, muc h le ss is k no wn ab o ut the i n fl u e n c e o f i m m u n o l o gi c a l fa c to r s i n r e l a ti o n to th e patho ge ne sis o f the asso c iate d se ptal he patic fib r o sis. Se ptal fib r o sis induc e d b y pig-se r um was c o nside r e d to have an immunological basis, because it did not form in animals rendered to le r ant to pig- se r um3. Sim ilar r e sults we r e o b taine d fo r the
C. he pa tic a-induc ed septal fibro sis by Lemo s et al1 1. Ho wever,
the me c hanisms o f fib r o sis pr o duc tio n, the immuno lo gic al fac to r s invo lve d, have no t ye t b e e n de te r mine d. It se e ms that suc h me c hanisms r un par alle l with the ab ility o f the ho st to de str o y the par asite s. Our pr e se nt findings sugge st that b o th the c apac ity to mo unt destr uc tive lesio ns against the par asites and the ability to pr o duc e septal fibr o sis c an be blo c ked by an e xc e ss o f wo r m-de r ive d antige ns o c c ur r ing dur ing r e pe ate d infec tions. Apparently humoral fac tors ( serum antibodies against
C. h e p a ti c a) ar e no t invo lve d, unle ss the y ac te d in a ne gative way, sinc e the ir c o nc e ntr atio n inc r e ase d in the se r um dur ing r e -infe c tio ns. The mo r pho lo gic al findings no w o b se r ve d ar e str ikingly similar to tho se in r ats made to ler ant to C. he pa ti c a
by neonatal c ontac t with the homologous antigens, as desc ribed by Lemos et al1 1. In both c ases there oc c urred interferenc e with
worm development and a marked dec rease in inflammation and fibrosis. It is hoped that these findings will c ontribute to c alling attentio n to the immuno lo gic al natur e o f C. he pa ti c a-induc ed se ptal fib r o sis in r ats and the r e b y stimulate fur the r studie s to c larify its mec hanisms.
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