Association between ambient air pollution and proliferation of umbilical cord blood cells.

It has been established as a common knowledge that ambient air pollution (AAP) has an adverse effect on human health. The pathophysiological mechanism of this impact is likely to be related to the oxidative stress. In the current study we estimate the association between AAP and cell proliferation (CP) of umbilical cord blood cells, representing maternal organism most proximal to the fetal body. Blood samples were tested for proliferation in 292 enrolled Arab-Bedouin women at delivery (July 2012-March 2013). The estimates of AAP were defined by a hybrid satellite based model predicting both PM2.5 (particles<2.5µm in diameter) and PM10 (particles<10µm in diameter) as well as monitoring stations for gaseous air pollutants. Risk estimates of pollution exposure were adjusted to medical history, household risk factors and meteorological factors on the day of delivery or one week prior. Ambient ozone (O3) levels on 1, 2, 3and 4 days prior to delivery were associated with lower CP (Prevalence ratio (PR)=0.92, 0.92, 0.93, 0.93, respectively). Increase in inter-quartile range (IOR) of PM2.5 one day before delivery was associated with 9% increase in CP levels (PR=1.09). The positive direction in association was changed to negative association with CP for PM2.5 levels measured at more distant time periods (PR=0.90 and 0.93 for lags 5 and 6 days, respectively). Investigation of PM10 levels indicated a similar pattern (PR=1.05 for pollution values recorded one day before delivery and 0.93 and 0.95 for lags of 5 and 6 days, respectively). Carbon monoxide (CO) levels were associated with lower CP on the day of delivery and 1day prior (PR=0.92 and PR=0.94). To conclude, the levels of cell proliferation of umbilical cord blood cells appear to be associated with the AAP. More studies are needed to support our findings.

Nitrogen Dioxide pollution and hazardous household environment: what impacts more congenital malformations.

Nitrogen Dioxide (NO2) is a product of fuel combustion originating mainly from industry and transportation. Studies suggest an association between NO2 and congenital malformations (CM). We investigated an independent effect of NO2 on CM by adjusting to individual factors and household environment in 1024 Bedouin-Arab pregnant women in southern Israel. This population is characterised by high rates of CMs, frequent consanguineous marriages, paternal smoking, temporary housing and usage of open fire for heat cooking. Information on household risk factors was collected during an interview. Ambient measurements of 24-h average NO2 and meteorological conditions were obtained from 13 local monitors. Median value of daily NO2 measured in the area was 6.78ppb. CM was diagnosed in 8.0% (82) of offspring. Maternal NO2 exposure during the 1st trimester >8.6ppb was significantly associated with minor CM (RR=2.68, p=0.029). Major CM were independently associated with maternal juvenile diabetes (RR=9.97, p-value=0.002) and heating by open fire (RR=2.00, p-value=0.049), but not NO2 exposure. We found that NO2 emissions had an independent impact only on minor malformations, whereas major malformations depended mostly on the household environment. Antepartum deaths were associated by maternal morbidity.

Impact of pooling on accuracy of hepatitis B virus surface antigen screening of blood donations.

Expenditure on screening blood donations in developing countries can be reduced by testing donations in pools. This study evaluated serological screening in pools for hepatitis B virus (HBV) at the Israeli national blood bank and a hospital blood bank in Gaza, the Palestinian Authority. The accuracy of HBV surface antigen (HBsAg) enzyme immunoassay performed on pools of 3-24 samples was compared with individual tests. Delay in detecting positive samples due to dilution in pools and the possibility of antibody-antigen neutralization were analyzed. The sensitivity of pooled testing for HBsAg was 93-99%, prolonging the window period by 5 days (8.3%). Neutralization of HBsAg by hepatitis B surface antibodies (anti-HBs) could be minimized by testing immediately after pooling. Serological testing for HBsAg in pools may be performed using manually created pools of up to six samples, with 5% loss in sensitivity and a risk of neutralization by anti-HBs present in the donor population. Pooling can therefore be considered as an option only in countries with a low prevalence of HBV.

Feasibility and cost-benefit of implementing pooled screening for HCVAg in small blood bank settings.

To examine the accuracy, feasibility and benefits of screening for hepatitis C virus core antigen (HCVAg) using enzyme-linked immunosorbent assay (ELISA) test in pools. Many countries cannot afford to test blood donations for hepatitis C using molecular methods. Screening individual units using the ELISA HCVAg test is an acceptable, yet still expensive, alternative, especially for small blood bank settings. This study evaluated the option of screening for HCVAg in pools. The sensitivity (Se) and specificity (Sp) of HCVAg in pools of three and six antibody-negative samples were estimated and compared with polymerase chain reaction (PCR). The feasibility and cost-benefit of the assay was assessed on 960 routine samples collected at a hospital blood bank in Gaza. Based on results for 50 PCR-positive pools and 50 and 110 PCR-negative pools of three and six, the Se of testing in pools of three and six samples is 80-82% [95% confidence interval (CI): 66.3-91.4] and Sp >or=98% (95% CI: 89.4-100.0) compared with PCR. The incidence of antigen in donors in Gaza was 0.1% (95% CI: 0-0.56). Cost analyses suggested significant benefits from implementing screening blood donations for HCVAg when the incidence rate is >4.2/10,000, leading to reduction in the expenditures needed to treat patients infected with HCV. The risk of transfusion-transmitted hepatitis C in resource-deprived developing countries can be efficiently reduced by additional screening of antibody-negative blood donations for HCVAg in pools of six.

Estimation of delay in detecting hepatitis C virus antibodies in pools compared to individual testing on seroconversion panels.

Testing for anti-hepatitis C virus (HCV) antibodies in pools may reduce blood screening costs, making this approach affordable for developing countries, provided that the dilution of infected blood does not significantly increase the number of undetectable viral particles, especially in seroconverters. This study assessed the delay in detection of HCV antibodies in five HCV seroconversion panels, tested in pools of 6-48 samples, and estimated the risk of transfusion-transmitted HCV caused by pooling. The delay in detection of positive samples was 5-12 days for pools of all sizes, adding 7% to the risk of HCV transmission that occurs when blood donors' samples are tested individually.

The role of trace elements in psoriatic patients undergoing balneotherapy with Dead Sea bath salt.

BACKGROUND: A beneficial effect was observed in patients with psoriasis vulgaris following balneotherapy with Dead Sea bath salt. OBJECTIVES: To evaluate the possible role of trace elements in the effectiveness of balneotherapy. METHODS: Serum levels of 11 trace elements were analyzed in 23 patients with psoriasis vulgaris who participated in a double-blind controlled study of balneotherapy with either Dead Sea bath salt (12 patients) or common salt (11 patients). Thirteen healthy volunteers served as controls. RESULTS: The mean pre-treatment serum levels of boron, cadmium, lithium and rubidium were significantly lower in patients compared to controls, whereas the mean pre-treatment serum level of manganese was significantly higher in patients compared to controls. Balneotherapy with Dead Sea bath salt resulted in a significant decrease (P = 0.0051) in the mean serum level of manganese from 0.10 +/- 0.05 mol/L to 0.05 +/- 0.02 mumol/L. The mean reduction in the serum level of manganese differed significantly (P = 0.002) between responders (% Psoriasis Area and Severity Index score reduction > or = 25) and non-responders (% PASI score reduction < 25). Following balneotherapy with Dead Sea bath salt the mean serum level of lithium decreased in responders by 0.01 +/- 0.02 mumol/L, whereas its level in non-responders increased by 0.03 +/- 0.03 mumol/L. (P = 0.015). CONCLUSIONS: Manganese and lithium may play a role in the effectiveness of balneotherapy with Dead Sea bath salt for psoriasis.

Prevalence of vectors of the spotted fever group Rickettsiae and murine typhus in a Bedouin town in Israel.

A survey of the vectors of spotted fever group Rickettsiae and of murine typhus was carried out in Rahat, a Bedouin town in the Negev Desert, where the diseases are endemic. Houses with known cases of spotted fever group Rickettsiae or murine typhus were compared with those without reported clinical cases. A neighboring Jewish community, Lehavim, where no cases of spotted fever group Rickettsiae and murine typhus were reported in recent years, was used as a control. In the houses of patients with spotted fever group Rickettsiae in Rahat, an average of 7.4 times more ticks were found than in control houses. Out of 190 ticks isolated from sheep and goats or caught by flagging in Rahat, 90% were Rhipicephalus sanguineus (Latreille), 7.9% Rhipicephalus turanicus Pomerantzev, and 2.1% were Hyalomma sp. In the houses of patients with murine typhus, three times more rats were caught and, on the average, each rat was infested with 2.2 times more fleas than rats in the control houses. Out of 323 fleas collected from 35 Norwegian rats (Rattus norvegicus Berkenhout), 191 were Xenopsylla cheopis Rothschild and 132 Echidnophaga murina Tiraboschi. Thus, there was a six to seven times higher probability of encountering a tick or flea vector where infections had occurred than in control houses in Rahat. The percentage of rats seropositive to Rickettsia typhi was similar in study and control households (78.3 and 76.2, respectively). In the control settlement, Lehavim, only three Mus musculus L. were caught, which were not infested with ectoparasites and their sera were negative for murine typhus. Out of 10 dogs examined in this settlement, 15 R. sanguineus and eight specimens of the cat flea (Ctenocephalides felis felis Bouché) were isolated. No rats were caught in this settlement. These data indicate that there is a correlation among the density of domestic animals, their ectoparasites, and the incidence of spotted fever group Rickettsiae and murine typhus in Rahat.

Which intercurrent infections are associated with maculopapular cutaneous drug reactions? A case-control study.

BACKGROUND: Patients with lymphotrophic viral infections are at increased risk for cutaneous drug reactions (CDRs). However, the association between other intercurrent infections and maculopapular CDRs has not been evaluated by epidemiologic methods. OBJECTIVE: We conducted a case-control study in order to evaluate the exposure to intercurrent infections in patients with maculopapular CDRs. METHODS: Data were obtained through assessment of files of 53 patients hospitalized for maculopapular CDRs in the Department of Dermatology and 159 control patients. Exposure to intercurrent infections was recorded in patients and controls. RESULTS: An intercurrent infectious disease was documented in 31/53 (58.5%) of patients with CDRs, as compared to 12/159 (7.5%) patients in the control group (OR 17.26, 95% CI: 7.24-42.00). Maculopapular CDRs were associated with respiratory tract infections (OR 20.53, 95% CI: 5.20-94.45), and urinary tract infections (OR 20.61, 95% CI: 2.36-465.99), but not with skin infections (OR 3.83, 95% CI: 0.85-17.87) or other infections. CONCLUSIONS: Our study implies that maculopapular CDRs are associated with respiratory tract infections as well as urinary tract infections. Further study is needed to evaluate the role of intercurrent infections in the pathogenesis of CDRs.

Seroepidemiology and molecular epidemiology of Kaposi's sarcoma-associated herpesvirus among Jewish population groups in Israel.

BACKGROUND: The incidence of classic Kaposi's sarcoma among Jews in Israel is among the highest in the developed world. Kaposi's sarcoma-associated herpesvirus (KSHV or human herpesvirus 8) is causally linked to Kaposi's sarcoma. Very little is known about the prevalence of KSHV in the Middle East or about the modes of transmission in Mediterranean countries. METHODS: From 1992 through 1995, sera were obtained from 1648 adults who had tested positive for hepatitis B virus (HBV) surface antigen 20 years earlier at blood donations; sera were also obtained from 2403 of their family members. All sera were tested for anti-KSHV antibodies with the use of an indirect immunofluorescence assay. To analyze the effects of various factors on the risk of KSHV infection for both the HBV-positive cohort and their families, logistic regression for cluster data and generalized estimating equations were used. All statistical tests were two-sided. RESULTS: Among family members, the seroprevalence of antibodies against KSHV was 9.9% (95% confidence interval [CI] = 8.7% to 11.1%); among the former blood donors who had tested positive for hepatitis B, it was 22% (95% CI = 19.9% to 24.1%). Overall, the best predictor of KSHV status was the place of birth. The most important risk factors found for both husband and wife to test KSHV positive were their own places of birth and their spouse's seropositivity. For a child to test positive, the most important risk factor was maternal seropositivity. CONCLUSIONS: The crude prevalence rate of KSHV among the Jewish population in Israel is 9.9%. Important routes of KSHV transmission in the families studied are spouse to spouse and mother to child. The presence of KSHV in Jews in Israel of all ethnic origins and their high incidence of reported Kaposi's sarcoma suggest that KSHV was introduced into the Jewish population prior to the major Diaspora.

HIV-1 IgA specific serum antibodies and disease progression during HIV-1 infection.

OBJECTIVE: To evaluate the role of serum human immunodeficiency virus type 1 immunoglobulin A (HIV-1 IgA) antibodies in the progression of HIV-1 infection in relation to viral load and CD4 cell counts. METHODS: Sequential serum specimens were obtained from 218 homosexual men: 123 HIV-1 seropositives, 24 HIV-1 seroconverters, and 71 HIV-1 seronegatives. HIV-1 IgA antibodies were tested blindly by enzyme-linked immunosorbent assay and Western blot. T-lymphocyte subsets were measured by flow cytometry. Viral plasma load was determined by a sensitive branched DNA assay. RESULTS: HIV-1 IgA antibodies with a titer greater than or equal to 50 were detected among 50% of the seroconverters, 27% of the HIV-1-seropositive asymptomatic subjects, 25% of lymphadenopathy, and 23% of HIV-1-related symptomatic subjects. Among patients with the acquired immune deficiency syndrome, the prevalence of virus-specific IgA antibodies (55%) was significantly higher (p < 0.03) as compared with the HIV-1-seropositive asymptomatic subjects, lymphadenopathy and HIV-1-related symptomatic patients, but not versus the seroconverters (p = 0.8). IgA antibodies to HIV-1 gP160 were the most prevalent among all subjects tested. A significant decrease in CD4 cell counts was observed after HIV-1 seroconversion. Viral load was slightly higher among the seroconverters who demonstrated higher (> or =50) HIV-1 IgA levels. CONCLUSIONS: HIV-1 IgA serum antibodies did not predict the progression of the disease. Correlation between HIV-1 IgA antibodies titer, viral load, and CD4 cell counts was not detected.

Prevalence of specific IgA and IgM anti-HBc antibodies compared with HBV DNA in the sera of HBsAg chronic carriers.

OBJECTIVE: We evaluated the significance of IgA antibodies directed against the hepatitis B virus core antigen (IgA anti-HBc) as a marker for viral replication. STUDY DESIGN/METHODS: Serum samples of 143 hepatitis B surface antigen (HBsAg) carriers and 189 HBsAg-negative subjects were studied. Hepatitis B virus (HBV) DNA was detected by polymerase chain reaction. IgA anti-HBc was determined by a capture enzyme-linked immunosorbent assay developed in our laboratory. The results were compared with those for IgM anti-HBc, which were determined by a commercially available method. RESULTS: IgA anti-HBc was detected in 57 (40%) and HBV DNA in 38 (27%) of the HBsAg carriers. Among the HBsAg-negative subjects, IgA anti-HBc and HBV DNA were detected simultaneously in four samples. All 42 HBV DNA-positive samples were IgA anti-HBc positive. IgM anti-HBc was detected in 27 (64%) of them. CONCLUSIONS: IgA anti-HBc is a sensitive marker for HBV replication, and its absence may exclude HBV replication. The role of IgA anti-HBc in monitoring response to therapy and predicting clinical course is being evaluated.

HBsAg confirmation: an experimental test.

BACKGROUND: The specificity of HBsAg testing is to be confirmed with antibody blocking to avoid false positive results. OBJECTIVE: To test the experimental HrAb HBsAg-blocking activity and to use this new antibody in the verification of repeatedly reactive HBsAg blood serum samples. STUDY DESIGN: HbsAg screening of three quality control panels was followed by a comparative confirmatory test with commercial HuAb and experimental HrAb. The HrAb was used in subsequent HBsAg confirmation trials. RESULTS: A good agreement in the results obtained using the two antibodies was found, independently of the type of HBsAg neutralization step performed (either preincubation or competitive inhibition). Of the 97 repeatedly reactive HBsAg blood serum samples, 79 were 'confirmed positives'. On repeated confirmations by two antibodies, 13/18 'not confirmed' converted to 'confirmed positives', while the same five samples still remained false positive. CONCLUSION: The results suggest that (1) HrAb is as good as HuAb in HBsAg confirmation and (2) HBsAg confirmatory testing is essential in the laboratory examinations of the HBsAg repeatedly reactive samples.

A combined community strategy to reduce cholesterol and other risk factors.

Our primary objective was to conduct an integrated program to reduce coronary risk factors in the population of an Israeli kibbutz. The population-based objective was to reduce the mean community total cholesterol level. The individual-based objective was to provide counseling and treatment for individuals at high risk and to reduce individual total and low-density lipoprotein cholesterol levels. The intervention included food policy changes in the central kibbutz kitchen, health education programs aimed at all age groups, and health counseling for individuals at risk. Evaluation was by questionnaire at baseline and at the end of two years, blood lipoproteins, and monitoring of all food purchased by the kibbutz. Fifty-three percent of the adult population (100 of 187) had borderline to high baseline total cholesterol levels. At one year, 27% of these were in the normal category. Egg consumption dropped by 6%, liquid oil by 7%, and red meat by close to 19%. Consumption of fish, chicken meat, and vegetarian patties increased. Consumption of 1% milk increased by almost 300%. We conclude that an integrated health education program targeting individuals and the community together can be effective in reducing risk factors for coronary artery disease.

Differences in cord serum retinol concentrations by ethnic origin in the Negev (southern Israel).

Subclinical vitamin A deficiency is related to increased morbidity and mortality in infants and children. Previous studies indicate that the traditional diet of Moslem Bedouins, an important ethnic group in Southern Israel, is low in vitamin A content. Cord serum retinol (vitamin A) concentration was measured by HPLC in samples from 251 apparently healthy (birth weight > 2500 g, gestational age > 37 weeks) neonates with no abnormal perinatal events, 138 Jews and 113 Bedouins. Retinol < 15 micrograms/dl was measured in a total of 14% of infants: in 7% of Jewish and 26% of Bedouin newborns (P < 0.001). However, mean cord serum retinol was only slightly lower in Bedouins than in Jews (30 +/- 26 vs. 37 +/- 27 micrograms/dl mean +/- S.D., n.s.). Cord serum retinol was not related to socioeconomic indices. Cord serum retinol < 15 micrograms/dl was measured in 25% and in 12% of infants with birth weight less than and equal or greater than 3000 g, respectively (P = 0.01), and in 28% and 13% of infants with gestational age 37-38 weeks and 39-41 weeks, respectively (P = 0.03). Low cord serum retinol was found to be prevalent in Southern Israel, particularly in Bedouin infants. In the population of healthy neonates studied, very low cord serum retinol concentrations were found more frequently in infants born with a lower weight and/or after a shorter gestation.

The significance of serum IgM IgA and IgG antibodies specific for Epstein-Barr virus as determined by immunoperoxidase assay in the rapid diagnosis of infectious mononucleosis.

The feasibility of using serum IgM, IgA and IgG antibodies specific to Epstein-Barr virus (EBV) viral capsid antigen (VCA), as determined by immunoperoxidase assay (IPA), for the early diagnosis of mononucleosis was evaluated in 65 patients with infectious mononucleosis (IMN). Control groups consisted of 104 healthy students and 15 cytomegalovirus-infected patients. In the first serum sample obtained upon admission, IgM antibodies (titer > or = 64) to EBV VCA were found in 64 of the 65 IMN patients (98%), while EBV-VCA IgA antibodies (titer > or = 32) were found in 32 patients (49%). In those particular titers, no EBV-VCA IgM or IgA antibodies were found in any of the control sera. EBV-VCA-specific IgM antibodies were also not detected in any of the 15 patients with cytomegalovirus infection. In sera obtained from IMN patients within 10 days of the onset of symptoms, 18 of 19 (95%) were IgM seropositive. This study demonstrates that serum EBV-VCA IgM antibodies (titer > or = 64) as determined by IPA are highly specific (100%) and highly sensitive (98%) and can be of value for the early and rapid diagnosis of EBV-IMN infection.

Altered humoral immunity against cytomegalovirus and Epstein-Barr virus without detectable virus antigens and virus-DNA in the glomeruli of patients with IGA nephropathy in remission phase.

Herpes viruses, such as cytomegalovirus (CMV) and Epstein-Barr virus (EBV), very often occur in the nasopharynx. A pathogenetic role of these viruses in immunoglobulin A nephropathy (IgA NP) is a challenging hypothesis, since upper respiratory tract infections are frequently and closely related in time to the acute episodes of IgA NP. However, conflicting reports have been published in this field. We compared the IgA and IgG antibody (AB) titres against cytomegalovirus (CMV) in sera of 41 IgANP patients with 80 healthy controls. The prevalence rates of CMV-IgA and CMV-IgG AB were significantly higher in patients with IgA NP than in healthy controls (CMV-IgA, titre > = 8, p < 0.001; CMV-IgG, titre > = 16, p < 0.05). There was also a significant difference in the concentration of CMV-IgA AB between IgANP patients and controls (IgA NP: 0.34 +/- 0.66, healthy controls: 0.06 +/- 0.33, mean +/- SD, p = < 0.002), but not in the concentration of CMV-IgG AB between NP patients and controls. While examining 60 patients with IgA NP and 75 healthy controls a significantly elevated prevalence rate of IgA AB against EBV capsid antigen (EBV-VCA) was also detected in the sera of IgA NP patients vs controls (titre > = 16; p < 0.05). There was no significant difference in the prevalence of IgG AB to EBV-VCA between patients with IgA NP and healthy controls, except at titre = 1024 (p < 0.05). At a follow-up, CMV-IgA persisted in 4 of 5, and EBV-VCA-IgA in 8 of 12 seropositive patients with IgA NP. We could not detect virus antigens or virus deoxyribonucleic acid (DNA) in the glomeruli of NP patients either with immunohistology using a monoclonal antibody or with the DNA in situ hybridization technique.(ABSTRACT TRUNCATED AT 250 WORDS)

Chlamydia specific IgG and IgA serum antibodies in a study of homosexual men at various clinical stages of HIV related disease.

The significance of chlamydia serum IgG and IgA antibodies was studied, by immunoperoxidase assay, in 210 homosexual men at various stages of HIV infection. Cross sectional analysis of chlamydia IgG antibodies at a titer of > or = 128 indicated a significantly higher prevalence rate among AIDS patients (27.0%) as compared to asymptomatic HIV seronegatives (6.0%) (p = 0.022). The geometric mean titer (GMT) of IgG antibodies to chlamydia was also significantly higher in AIDS patients (106.4) as compared to HIV seronegatives (58.2) (p = 0.022) and persistently asymptomatic HIV seropositives (51.7) (p = 0.05). Chlamydia IgA antibodies did not differ significantly in prevalence and GMT among the various groups.

Chlamydia trachomatis and HIV infection.

To study the interactions between Chlamydia trachomatis (CT) and human immunodeficiency virus (HIV) infections, we examined CT serologies in sequential serum samples of male homosexuals (MHS), followed over a mean period of 4 years. Of the MHS studied, 77 were HIV(-), 18 were HIV(+) and 10 patients seroconverted during the study period. Seventy matched heterosexual controls were tested concomitantly. CT-specific antibodies of both IgG and IgA isotypes were determined by an immunoperoxidase assay, indicating past and active infection respectively. Anti-CT IgG was frequently observed in both HIV(-) and HIV(+) MHS (40-50% vs. 23% of controls) and IgA antibodies were also common in both MHS groups (15-20% vs. 1.5% of controls). After HIV infection, no increase in CT antibodies occurred. We found serological data suggestive of active CT infection preceding seroconversion in 3 of 10 seroconverters vs. 5% of matched MHS controls who remained HIV(-) (P < 0.025), indicating a possible effect of CT infection on the acquisition of HIV should be further studied.

Serum reactivity to Chlamydia trachomatis and C. pneumoniae antigens in patients with documented infection and in healthy children by microimmunofluorescence and immunoblotting techniques.

Chlamydia trachomatis and C. pneumoniae are both important human pathogens. Antigenic cross-reactivity between the two species may complicate serologic diagnosis of infection with one or the other agent. In this study we examined sera of persons with chlamydia infections and of healthy children by microimmunofluorescence (MIF) against C. trachomatis L2 antigen and against C. pneumoniae TW-183 antigen to explore the degree of cross-reactivity found by these two methods. Likewise, the cross-reactivity seen by immunoblot with sera of rabbits immunized against one of the antigens when tested on the other was examined. While among healthy children stratified by age, MIF seropositivity to C. pneumoniae TW-183 increased with age, no such trend was observed with respect to seropositivity to C. trachomatis L2 antigens, and 81% of children seropositive to TW-183 did not react on L2 antigen. Moreover, 27% of those positive on L2 antigen were negative on TW-183. Immunoblot analysis showed much greater antibody cross-reactivity than that detected by MIF. The immunoblot cross-reactivity was probably not attributable solely to double infection since sera of rabbits immunized to only one species of chlamydia reacted strongly with both chlamydiae in immunoblot analysis. The data presented need to be taken into account in the development of serologic tests based on a small number of antigens or on partially denatured antigens.