Determination of IgG avidity is useful to distinguish primary infection from reactivation or reinfection in viral, parasitic or bacterial infections. For diagnosis of HIV type 1 primary infection, the detection of IgM antibodies is often useless since they are also found in chronic infection. The usual serology (Elisa, western-blot, p24 antigen) may present no interest if done too late (more than 2 or 3 months after infection). Therefore, we have developed a test to determine the avidity of anti-HIV1 antibodies, using 1 M guanidine as denaturing agent. We have adapted the measurement of avidity to the Axsym automatic system for a routine use. Indeed, since requests for avidity determinations are sporadic, the use of microplates is not convenient. Using this assay, we found a low avidity (less than 50%) in immunocompetent and recent infected patients (less than 6 months), compared to old infected patients (more than 12 months) who had high avidity (80 to 100%). However, early treated patients (in the 6 months after contamination) had also low avidities but with a slower development of antibody maturation (8 to 27 months versus 2 to 8 months in non treated patients). To conclude, the determination of the anti-HIV1 avidity, according to the proper procedures explained here (notion of treatment and/or serious immunodepression), may help the physician to date the infection in each new infected patient who might benefit from an early treatment.

Transfusion. 2003 Jul;43(7):958-62.
A new HCV core antigen assay based on disassociation of immune complexes: an alternative to molecular biology in the diagnosis of early HCV infection.
Laperche S, Le Marrec N, Simon N, Bouchardeau F, Defer C, Maniez-Montreuil M, Levayer T, Zappitelli JP, Lefrere JJ.
Department of Blood Transmissible Agents, National Institute of Blood Transfusion, Paris, France.

BACKGROUND: An EIA based on immune complex disassociation of nucleocapsid proteins of HCV has been developed to detect and quantify HCV core antigen. STUDY DESIGN AND METHODS: To evaluate whether this new assay (trak-C, Ortho Clinical Diagnostics) could be an alternative to NAT during the window period, its sensitivity in this context was assessed, and its performance was compared with that of a first-generation HCV core antigen assay dedicated to the blood screening (HCV core antigen ELISA). Studied populations included nine HCV RNA-positive, HCV antibody-negative blood donors and 23 hemodialysis patients who underwent an HCV seroconversion. From these individuals, 81 samples (23 HCV RNA-negative and 58 HCV RNA-positive) sequentially collected during the phase before seroconversion were tested. RESULTS: The nine blood donor samples were positive for the presence of HCV core antigen by the trak-C, and 6 of 8 tested were positive for the presence of HCV core antigen by blood screening ELISA. In the hemodialysis cohort, the 23 HCV RNA-negative samples were negative with the two HCV core antigen assays. Among the 58 HCV RNA-positive samples, 46 of 57 (80.7%) tested were positive for the presence of HCV core antigen with the blood screening assay, and 57 of 58 (98.2%) were positive for the presence of HCV core antigen with the trak-C. The mean delays in detecting HCV infection between trak-C and the appearance of HCV antibodies, between HCV RNA testing and trak-C, and between trak-C and HCV core antigen ELISA were 58.2, 0.24, and 3.33 days, respectively. CONCLUSION: Trak-C was more sensitive than the blood screening assay and had similar performance to HCV RNA assay in the window period. Trak-C could constitute an alternative to NAT for the diagnosis of HCV infection during the window period, especially when molecular biology procedures cannot be implemented.

Scand J Infect Dis Suppl. 1993;89:3-62.
Herpes simplex encephalitis. Early diagnosis and immune activation in the acute stage and during long-term follow-up.
Aurelius E.
Department of Infectious Diseases, Karolinska institute, Danderyd Hospital, Sweden.

From a series of in all 93 patients with herpes simplex encephalitis (HSE), verified by biopsy and/or the demonstration of intrathecal synthesis of antibodies to the virus, cerebrospinal fluid (CSF) and serum samples were analysed and compared with samples from 80 patients with non-HSE, i.e. acute encephalitis of non-HSV origin (approximately 50% with other known aetiology, 50% of unknown origin) treated on the suspicion of HSE but in whom no signs of intrathecal HSV antibody synthesis were found, and samples from an additional 42 patients with other verified or suspected diseases of the CNS. To improve the early non-invasive diagnosis of HSE, a HSV IgG capture enzyme linked immunosorbent assay (ELISA) was developed to demonstrate intrathecal synthesis of antibodies to the virus and the results were compared to those of the indirect ELISA. The capture ELISA was found to be advantageous in detecting the early antibody response and yielded more clear-cut results. No correction for damage to the blood-CSF barrier was needed and the method was therefore less labour-intensive than the indirect ELISA. Furthermore, a polymerase chain reaction (PCR) assay, with two "nested" primers pairs selected in the glycoprotein D gene of HSV-1, was developed for the amplification of HSV DNA in CSF. The method was found to be a rapid and non-invasive means of diagnosing HSE in a very early stage of the disease; it was highly sensitive and specific. With a combination of nested PCR assays for HSV-1 and HSV-2 (primers in the glycoprotein G gene) in 10 microliters of CSF, HSV DNA was detected in CSF from 88 out of 93 patients (95%) with HSE. Evidence of HSV-2 aetiology was found in 6 of 93 consecutive cases of HSE in immunocompetent patients by type-specific assays for the demonstration of HSV-2 DNA (primers in the gG gene) and HSV-2 antibodies (to gG2 antigen) in the CSF. Five of the 6 patients with HSV-2 encephalitis exhibited a clinical picture of severe HSE indistinguishable from that of "classical" HSV-1 encephalitis. The combined use of PCR for the detection of HSV DNA in the CSF and the demonstration of intrathecal synthesis of antibodies to the virus will yield a reliable diagnosis and is now the method of choice for the diagnosis of HSE.

Haematologica. 2002 Oct;87(10):1046-52.
Attempt to improve the diagnosis of immune thrombocytopenia by combined use of two different platelet autoantibodies assays (PAIgG and MACE).
Fabris F, Scandellari R, Randi ML, Carraro G, Luzzatto G, Girolami A.
Department of Medical and Surgical Sciences, University of Padua Medical School, Italy.

BACKGROUND AND OBJECTIVES: Despite an extensive search for a definitive diagnostic assay for platelet autoantibodies, the laboratory diagnosis of immune thrombocytopenia (ITP) still remains a clinical challenge. Data in the literature have so far demonstrated that measurement of platelet-associated IgG (PAIgG) is sensitive, especially when flow cytometry is employed, but lacks adequate specificity. Measuring specific autoantibodies by antigen capture techniques increases specificity, but a large part of patients escape autoantibodies detection by such means too. The aim of the present study was to compare the diagnostic value of PAIgG with a modified antigen capture ELISA (MACE) in patients with primary and secondary immune thrombocytopenia and in patients with non-immune thrombocytopenia. DESIGN AND METHODS: One hundred and four patients with a platelet count lower than 100x109/L were studied. Forty-two patients had primary ITP (P-ITP), 23 patients had ITP secondary to other immune diseases (S-ITP) and 39 patients had thrombocytopenia due to decreased platelet production (non-immune; NITP). PAIgG was measured by immunofluorescent flow cytometry, whereas specific platelet-associated autoantibodies (against GP IIb/IIIa, Ib/IX, Ia/Ia) were measured by a commercially available modified antigen capture assay (MACE, GTI, USA). RESULTS: The sensitivity of the PAIgG assay for ITP was 60%, the specificity was 77%, the positive predictive value was 81% and the negative predictive value was 54%. The sensitivity of MACE was 60%, specificity was 97%, the positive predictive value 97% and the negative predictive value 59%. We found a 73% concordance between PAIgG and MACE assays. Both PAIgG and MACE had significantly greater sensitivity in S-ITP than in P-ITP. INTERPRETATION AND CONCLUSIONS: Forty percent of patients with clinically diagnosed immune thrombocytopenia had no detectable platelet autoantibodies, possibly because of intrinsic methodological detection problems, different stages of disease, or absence of a true immune etiology.

Rev Med Brux. 2001 Apr;22(2):73-82
Immune deficiencies: diagnosis, management, some perspectives
Farber CM, Benoit Y, Boven K, De Baets F, Ferster A, Hoyoux C, Mascart F, Otten J, Philippet P, Van Lierde S, Van Vooren JP, Vermylen C.
Hopital Erasme Unite de Traitement des Immunodeficiences Route de Lennik 808 1070 Bruxelles.

Severe primary immunodeficiencies (PID) are rare; their global incidence is comparable to that of childhood leukemia; they include more than 100 different entities. Clinical manifestations are: unusually severe or frequent infections or infections that do not respond to adequate treatment; an increased risk of certain malignancies; sometimes auto-immune manifestations. Delayed diagnosis and management of PID can lead to severe and irreversible complications or to death. PID can become manifest only in the adult; in common variable immune deficiency, the median age at diagnosis is between the 2nd and the 3rd decade of life. PID are often transmitted genetically; recent progresses in molecular biology have allowed more precise and earlier, including antenatal, diagnosis. Molecular treatment of 3 infants with a severe immunodeficiency has recently been achieved in April 2000. Those progresses were mostly based on the study of immunodeficiency databases. We present here the work of a Belgian group specialized in PID; meetings have started in June 1997. This group establishes guidelines for the diagnosis and treatment of PID, adapted to the local situation. The elaboration of a national register of PID is also underway; this has to provide all guaranties of anonymity to patients and families. Such a register already exists at the European level; it has provided the basis for new diagnostic and therapeutic possibilities. The inclusion of Belgian data in this register should allow essential progresses essential for our patients.