1280

IS ANTIPATERNAL CYTOTOXIC ANTIBODY AVALID MARKER IN THE MANAGEMENT OF

RECURRENT ABORTION?

SiR,—Reports of successful pregnancy outcome followingimmunisation with partners’ lymphocytesl-4 are creating publicdemand for the routine introduction of such treatment for womenwith a history of recurrent spontaneous abortion. The rationale isthat such women have an immunological deficiency that preventsthem from mounting an appropriate response to protect theirallogeneic fetus. The nature of this response is unknown, as is themechanism whereby immunisation might confer benefit.

Nevertheless, most centres offering such treatment insist that theirpatients do not have circulating anti-patemal cytotoxic antibodies(APCA) before immunisation, implying that the absence of thisantibody is significant in the aetiology of recurrent abortion. Forexample, Mowbray et al4 state that "only those women with noantibodies to paternal T and B lymphocytes were offered treatment,on the basis that they had not shown the normal antibody responseto repeated pregnancies". Furthermore, these authors suggest thatwomen who seroconvert after their white cell infusion have an

improved subsequent pregnancy outcome, and that this

immunological "protection" persists for up to 12 months. In

contrast, patients who remain APCA negative and conceive morethan 80 days after treatment are likely to miscarry again and shouldbe offered booster injections. If the development of cytotoxicantibody is a prerequisite for successful pregnancy outcome, whyhad 55 % of the treated women who went on to have a successful

pregnancy4 never produced cytotoxic antibodies? Moreover, theincidence and significance of such antibodies in normal pregnancyhave not been published, which renders the clinical assumptionsunjustified.

In our prospective study of the incidence of APCA in a normalpregnant population we have so far recruited 456 women, who haveagreed to give us a pre-pregnancy blood sample, a second sample assoon as they become pregnant, and samples at 10-12, 18, 28, 32weeks’ gestation, at delivery, and at 4 weeks’ post partum. Paternalblood is obtained at the final post-partum visit, after which

cytotoxicity testing4,5 of the frozen sera is done.Of the 226 pregnancies declared to date, 130 have resulted in live

births and 23 have aborted spontaneously. There have been 1

therapeutic termination for fetal abnormality and 2 ectopicgestations. 70 pregnancies are still in progress.The APCA status of the 141 pregnancies which have reached the

postpartum testing point is as follows:

62 % of patients who had live births never produced detectablecytotoxic antibody during pregnancy, demonstrating that APCAare not necessary for successful pregnancy. The correspondingfigure for the women in the miscarriage group was 90%, which

‘

might be interpreted as support for a lack of antibody being causallyrelated to spontaneous abortion. That this conclusion is incorrectcomes from a consideration of the time course of antibodydevelopment in relation to the time of spontaneous abortion.The cumulative frequency and gestational time of development

of cytotoxic antibody in the 120 women with live births is shown inthe figure. Of the 38 % of women with live births who producedantibody, most became positive after 28 weeks’ gestation, with theincidence peaking at the delivery interval. Only 4 patients hadantibody present in their pre-pregnancy blood sample; in 3 thedevelopment of allogeneic antibodies could be explained by bloodtransfusions (2) and an ectopic pregnancy (1). Only 4 patientsdeveloped antibody before 14 weeks. All 23 of the women on ourprogramme who had spontaneous abortions miscarried before 14weeks. These results suggest that the low incidence of antibody inour spontaneously aborting group arose simply because they hadinsufficiently long gestations to produce a response.The early results from our study suggest that detectable

circulating APCA is not necessary for the maintenance of

pregnancy. Neither does it provide a reliable marker for a pregnancythat is destined to be successful. Absence of APCA can no longer be

Cumulative frequency of antibody development.related causally to a tendency to recurrent abortion. The temptationto use this antibody to monitor immunisation treatment and predictpregnancy outcome should be resisted until its significance is fullyunderstood.

We wish to thank Dan Hill, Janet Currie, and Anne Cant for technicalassistance and Martin Johnson for helpful advice. Supported by an MRCprogramme grant to P. R. B. and Dr M. H. Johnson.

Embryo and Gamete Research Group,Department of Obstetrics and Gynaecology,University of Cambridge Clinical School,Rosie Maternity Hospital,Cambridge CB2 2SW

LESLEY REGANPETER R. BRAUDE

1. Taylor C, Faulk WP Prevention of recurrent abortion with leucocyte transfusions.Lancet 1981; ii: 68-70.

2. Beer AE, Semprini AE, Ziaoyu Z, Quebberman JF. Pregnancy outcome in humancouples with recurrent spontaneous abortions HLA antigen profiles; HLA antigensharing; Female serum MLR blocking factors; and paternal leukocyteimmunisation. Exp Clin Immunogenet 1985; 2: 137-53.

3. Mowbray JF, Gibbings C, Liddell H, Reginald PW, Underwood JL, Beard RW.Controlled trial of treatment of recurrent spontaneous abortion with paternal cells.Lancet 1985; i: 941-43.

4. Mowbray JF, Underwood JL, Michel M, Forbes PB, Beard RW. Immunisation withpaternal lymphocytes in women with recurrent miscarriage. Lancet 1987; ii:

679-805. Mittal KM, Mickey MR, Singal PP, Terasaki PI. Serotyping for homotransplantation

XVIII: Refinement of microdroplet lymphocyte cytotoxicity test. Transplantation1969, 6: 904-12.

LACTTTOL, LACTULOSE, AND BLOOD AMMONIA

SIR,-Dr Douwes and colleagues (Sept 19, p 688) go some way tocorrecting the omission in your editorial (July 11, p 81) on lactitoland lactulose of reference to their inhibitory effect as bacterialsubstrates in reducing bacterial ammoniagenesis;l this is probablythe main explanation for the reduced intestinal generation ofammonia in patients taking lactulose?.3

Bacteria, including those in the intestine, use ammonia as apreferred nitrogen source in the synthesis of aminoacids-,’ they alsogenerate ammonia by deamination of arninoacids,s the main sourceof ammonia within the large bowel lumen .6 Within the intestinethere is normally a shortage of bacterial substrate in relation tobacterial numbers, with the result that ammonia production fromdeamination exceeds ammonia use, leading to net bacterial

generation of ammonia.7 This catabolic state can be reversed byprovision of bacterial substrate in the form of fermentable

carbohydrate, which lowers intestinal ammonia by two separate butcomplementary mechanisms-it promotes ammonia incorporationby bacteria (ref 1 and Douwes et al), and it decreases production ofammonia by a complex action of inhibition of the activity ofpreformed bacterial deaminases and of the formation of furtherenzyme.8,9 These actions of substrate depend on its incorporationinto the organism’s own glycolytic pathways, and are therefore inproportion to the abililty of a bacterium to metabolise the substrate.

Lactulose is rapidly fermented by intestinal bacteria and whenpresent in an incubation system it can lead to the disappearance ofammonia, a process independent of its simultaneous action inacidifying the medium. Glucose behaves similarly, as do the sugaralcohols mannitol, sorbitol, and xylitol (ref 1 and Douwes et al).Fermentable forms of plant fibre, such as pectin and the