Naidoo, Shalena (2012-03)
ENGLISH ABSTRACT: Background: In South Africa alone, 30% of women of child-bearing age are infected with HIV. With the increasing focus and success of prevention of mother-to-child transmission (PMTCT) programmes, an estimated 300 000 infants are born exposed to HIV every year. The underlying impact of in utero HIV exposure on infant immune health has not been extensively characterised. Clinical follow-up of these HIV-exposed uninfected (HEU) infants reveals increased infectious morbidity and mortality compared to their unexposed (UE) counterparts. Objectives: (i) To evaluate and characterise adaptive immune properties by measuring vaccine-specific antibody levels in children from 2 weeks to 2 years of age in the presence and absence of maternal HIV infection. (ii) To investigate specific cellular markers of immune activation, immune regulation, apoptosis and B cell memory on T and B cell populations in HEU and UE children measured at 18 and 24 months of age. Methods: This sub-investigation formed part of a collaborative pilot study between the universities of British Columbia (Vancouver, Canada) and Stellenbosch. A total of 95 HIV-positive and HIV-negative mothers were recruited after delivery at Tygerberg Hospital, and signed informed consent for their infants to be included in the study. Of these infants, only 27 HEU and 30 UE infants were eventually enrolled and followed up at various time points, starting at two weeks of age. Four of these infants were confirmed to be HIV-positive at 2 weeks and clinically followed up according to the protocol, but were excluded from statistical data analyses. Blood was collected at 2, 6 and 12 weeks and again at 6, 12, 18 and 24 months of age. Quantitative IgG-specific antibodies to Haemophilus influenzae B (Hib), Bordetella pertussis, tetanus and pneumococcus were measured at each time point, using commercially available ELISA (Enzyme-Linked ImmunoSorbent) kits. Cellular markers of immune activation, immune regulation, apoptosis and memory were measured in various populations of T and B cells at 18 and 24 months only, by using four-colour flow cytometry and validated whole-blood staining methods. In addition, a functional assay was developed to evaluate cell susceptibility to apoptosis (spontaneously) by measuring the expression of Annexin V on both CD4+ T and CD20+ B cells after 16 and 24-hour incubation periods. The statistical analysis of the antibody data was conducted by repeated-measures ANOVA (i.e. analysis of variance), using a mixed-model approach. Differences in the expression of the two groups’ cellular markers were compared by employing one-way ANOVA. An F test p value (which assumes normality) was reported, while the non-parametric Mann-Whitney U test served as confirmatory tool. Repeated-measures ANOVA was used for the evaluation of the functional spontaneous apoptosis assay at three time points (ex vivo, 16 and 24 hours) on the 18-month samples, while one-way ANOVA was used for the 24-month samples. Results: The HEU group (n = 23) displayed significantly lower levels of antibodies to pertussis (20.80 vs 28.01 Food and Drug Administration [FDA] U/ml; p = 0.0237), tetanus (0.08 vs 0.53 IU/ml; p < 0.001) and pneumococcus (31.67 vs 80.77 mg/l; p = 0.003) than the UE group (n = 23) at 2 weeks of age. No statistical differences were noted for Hib antibody levels between the two groups at this time point. At 6 weeks of age, HEU infants displayed lower mean levels of all antibodies measured; however, these differences did not reach statistical significance.
Following vaccination, compared to UE controls, the HEU group presented with statistically significantly higher antibody levels to pertussis at 6 months (155.49 vs 63.729 FDA U/ml; p = 0.0013), 12 months (26.54 vs 8.50 FDA U/ml; p < 0.001) and 18 months of age (1658.94 vs 793.03 FDA U/ml; p = 0.0362). A significant difference in tetanus antibody levels between the two groups was only evident at 24 months, with the HEU group displaying higher levels (3.28 vs 1.70 IU/ml; p = 0.018) than the UE group. No differences were observed between the two groups following vaccination for Hib. At 18 and 24 months, the HEU group showed increased expression of cellular markers of immune activation (CD69 and CD40L) on CD4+ T cells compared to UE controls. The two groups showed similar expression of the cellular marker of activation CD38 on CD8+ T cells. The HEU group displayed significantly higher levels of CD127, the interleukin (IL) 7 receptor, on CD4+ T cells compared to UE controls at 18 months of age. The HEU group also showed increased expression of cellular markers of apoptosis on both CD4+ T and CD8+ T cells. No statistical significance was noted for the expression of Fas on CD4+ T cells at 18 and 24 months of age. However, at 24 months, the HEU group showed significantly increased expression of FasL on both CD4+ T and CD8+ T cells. During cell culture experiments, the HEU group displayed increased susceptibility to spontaneous apoptosis shown by increased Annexin V expression on CD4+ T cells after a 16-hour incubation period at both 18 and 24 months. At 18 and 24 months, no difference was noted in the two groups’ immune regulation as measured by the expression of CTLA-4. The HEU group displayed increased levels of the cellular markers of immune activation CD80 on CD20+ B cells at 18 and 24 months of age. The HEU group also showed significantly increased levels of CD69 on CD19+ B cells at 24 months. No statistical significance was reached for the expression of CD62L and CD10 at either 18 or 24 months. Although the HEU group displayed increased levels of apoptosis (Fas) on CD20+ B cells, no statistical significance was reached at 18 or 24 months of age. In addition, the HEU group showed no difference in the expression of programmed death 1 (PD-1) at 18 and 24 months. HEU and UE groups showed similar expression of Annexin V after 16 hours of incubation in the 18 and 24-month samples. The expression of the biomarker of B cell memory CD27 on CD20+ B and CD19+ B cells was comparable between the two groups at both time points. Conclusion: At 2 and 6 weeks, lower mean antibody responses in HEU infants suggest poor placental transfer due to maternal HIV infection, while increased responses to specific antibodies may reflect an exaggerated immune response to immunisation. These robust responses may be due to the lack of competition with maternal antibodies, or may be ascribed to indirect stimulation of B cells via the activation of T cells. A hyper-inflammatory state is an imminent danger, with increased expression of cellular markers of immune activation and apoptosis that may be consistent with early HIV exposure that persists following infancy. These observations may serve as contributing factors to the extensively documented increased susceptibility to infections in the HEU population. Although these findings are consistent with a primed immune system, larger studies are required to confirm these observations in relation to clinical outcomes and to assess further whether these differences persist in later years.
AFRIKAANSE OPSMOMMING: Agtergrond: In Suid-Afrika alleen het 30% van vroue van ŉ vrugbare leeftyd MIV. Met die toenemende fokus en sukses van programme vir die voorkoming van moeder-na-kind-oordrag (sogenaamde PMTCT-programme) word ongeveer 300 000 babas jaarliks aan MIV blootgestel. Die onderliggende impak van intra-uteriene MIV-blootstelling op ŉ baba se immuunstelsel is nog nie omvattend beskryf nie. Kliniese opvolgondersoeke van hierdie MIV-blootgestelde dog onbesmette babas (sogenaamde HEU’s) dui op ŉ hoër siekte- en sterftesyfer weens infeksies as hul nieblootgestelde eweknieë (sogenaamde UE’s). Doelstellings: (i) Om kinders met MIV-positiewe en MIV-negatiewe moeders se aangepaste (verworwe) immuuneienskappe te beoordeel en te beskryf deur hulle vaksienspesifieke teenliggaamvlakke vanaf die ouderdom van twee weke tot twee jaar te meet. (ii) Om ondersoek in te stel na bepaalde sellulêre merkers van immuunaktivering, immuunregulering, apoptose en B-selgeheue by die T- en B-selgroepe van sowel HEU’s as UE’s op die ouderdom van 18 en 24 maande. Metodes: Hierdie subondersoek het deel uitgemaak van ŉ samewerkende loodsondersoek tussen die universiteite van Brits-Columbië (Vancouver, Kanada) en Stellenbosch. Altesaam 95 MIV-positiewe en MIV-negatiewe moeders is gewerf nadat hulle by Tygerberghospitaal geboorte geskenk het, en het ingeligte toestemming verleen dat hul babas by die studie ingesluit kon word. Van dié babas is slegs 27 HEU’s en 30 UE’s uiteindelik in die studie opgeneem en in verskillende stadia vanaf die ouderdom van twee weke opgevolg. Vier van die babas is op twee weke as MIV-positief bevestig en volgens die protokol klinies opgevolg, maar is van die statistiese dataontleding uitgesluit. Bloedmonsters is op twee, ses en 12 weke en weer op ses, 12, 18 en 24 maande geneem. Kwantitatiewe IgG-spesifieke teenliggame teen Haemophilus influenzae B (Hib), Bordetella pertussis, tetanus en pneumokokkus is telkens met behulp van kommersieel verkrygbare ELISA- (“Enzyme-Linked ImmunoSorbent”-)stelle bepaal. Sellulêre merkers van immuunaktivering, immuunregulering, apoptose en geheue is op slegs 18 en 24 maande by verskillende populasies T- en B-selle deur middel van ŉ vierkleurvloeisitometrie en geldig verklaarde volbloedkleuringsmetodes bepaal. Voorts is ŉ funksionele toets ontwikkel om selvatbaarheid vir apoptose te bepaal deur die ekspressie van Annexin V op sowel CD4+ T- as CD20+ B-selle ná 16 en 24 uur van inkubasie te meet. Die statistiese ontleding van die teenliggaamdata is met behulp van herhaaldemetings-ANOVA (d.w.s. afwykingsontleding) volgens ŉ gemengdemodel-benadering gedoen. Verskille in die twee groepe se sellulêre merkervlakke is deur middel van eenrigting-ANOVA vergelyk. ŉ F-toets-p-waarde (wat normaliteit veronderstel) is bereken, terwyl die nieparametriese Mann-Whitney-U-toets as bevestigende instrument gedien het. Vir die 18 maande-monsters is herhaaldemetings-ANOVA gebruik om die funksionele toets vir spontane apoptose in drie stadia (ex vivo, op 16 uur en op 24 uur) te beoordeel. Vir die 24 maande-monsters is eenrigting-ANOVA gebruik. Resultate: Op die ouderdom van twee weke het die groep HEU’s (n = 23) aansienlik laer teenliggaamvlakke teen kinkhoes (20.80 vs 28.01 Food and Drug Administration [FDA] U/ml; p = 0.0237), tetanus (0.08 vs 0.53 U/ml; p < 0.001) en pneumokokkus (31.67 vs 80.77 mg/l, p = 0.003) as die UE-groep (n = 23) getoon. In dié stadium is geen statistiese verskille in Hib-teenliggaamvlakke tussen die twee groepe opgemerk nie. Op ses weke het die groep HEU’s laer gemiddelde vlakke van ál die betrokke teenliggame getoon, hoewel hierdie verskille nie statisties beduidend was nie.
In vergelyking met die UE-kontrolegroep het die groep HEU’s ná inenting statisties beduidend hoër teenliggaamvlakke teen kinkhoes getoon op ses maande (155.49 vs 63.729 FDA U/ml; p = 0.0013), 12 maande (26.54 vs 8.50 FDA U/ml; p < 0.001) én 18 maande (1658.94 vs 793.03 FDA U/ml; p = 0.0362). ŉ Beduidende verskil in die twee groepe se tetanus-teenliggaamvlakke het eers op 24 maande geblyk, met die groep HEU’s s’n hoër (3.28 vs 1.70 IE/ml; p = 0.018) as die UE’s s’n. Ná inenting teen Hib is geen verskille tussen die twee groepe waargeneem nie. Op 18 en 24 maande het die HEU’s verhoogde ekspressie van sellulêre merkers van immuunaktivering (CD69 en CD40L) op CD4+ T-selle getoon in vergelyking met die UE-kontrolegroep. Soortgelyke vlakke van die sellulêre merker van aktivering CD38 is ook op die CD8+ T-selle van die twee groepe opgemerk. Op 18 maande het die HEU-groep ŉ beduidend verhoogde ekspressie van CD127, die IL-7-reseptor, op CD4+ T-selle getoon in vergelyking met die UE-kontrolegroep. Die HEU groep het ook verhoogde ekspressie van sellulêre merkers van apoptose op sowel CD4+ T- as CD8+ T-selle getoon. FAS-ekspressie op CD4+ T-selle op 18 en 24 maande was nie statisties beduidend nie, hoewel die HEU-groep op 24 maande beduidend verhoogde ekspressie van FasL op CD4+ T- sowel as CD8+ T-selle getoon het. In selkwekingseksperimente het die HEU-groep ŉ verhoogde vatbaarheid vir apoptose getoon na aanleiding van die ekspressie van Annexin V op CD4+ T-selle ná 16 uur van inkubasie op sowel 18 as 24 maande. Op 18 en 24 maande was immuunregulering, aan die hand van die ekspressie van CTLA-4, bykans dieselfde by albei groepe. Op sowel 18 as 24 maande toon die HEU’s verhoogde ekspressie van die sellulêre merker van immuunaktivering CD80 op CD20+ B-selle. Op 24 maande het die HEU’s ook aansienlik hoër vlakke van CD69 by CD19+ B selle getoon. Op nóg 18 nóg 24 maande was die ekspressie van CD62L en CD10 statisties beduidend. Hoewel verhoogde vlakke van apoptose (Fas) by CD20+ B-selle by die HEU-groep opgemerk is, was dit nie statisties beduidend op 18 óf 24 maande nie. Daarbenewens was daar ook geen verskil in die ekspressie van geprogrammeerde seldood 1 (PD-1) op 18 en 24 maande nie. Op 18 en 24 maande het die HEU’s en UE’s ŉ soortgelyke ekspressie van Annexin V ná 16 uur van inkubasie getoon. Op sowel 18 as 24 maande was die twee groepe se ekspressie van die biomerker van B-selgeheue CD27 op CD20+ B- en CD19+ B-selle vergelykbaar. Gevolgtrekking: Op twee en ses weke dui laer gemiddelde teenliggaamreaksies by HEU’s op swak plasentale oordrag weens die moeder se MIV-infeksie, terwyl verhoogde reaksies op bepaalde teenliggame weer op oordrewe immuunreaksie op inenting dui. Hierdie robuuste reaksie kan toegeskryf word aan die gebrek aan mededinging met die moeder se teenliggame, of kan deur indirekte stimulasie van die B-selle via die aktivering van die T-selle veroorsaak word. ŉ Hiperinflammatoriese toestand is ŉ dreigende gevaar, met verhoogde ekspressie van sellulêre merkers van immuunaktivering en apoptose wat met vroeë MIV-blootstelling met ŉ latere nawerking verbind kan word. Hierdie waarnemings kan bydraende faktore wees tot HEU’s se goed gedokumenteerde verhoogde vatbaarheid vir infeksies. Hoewel hierdie bevindings met ŉ geaktiveerde immuunstelsel strook, moet groter studies dit aan die hand van kliniese uitkomste bevestig en ook bepaal of hierdie verskille in later jare voortduur.
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