Internal quality control and external quality assurance in testing for antiphospholipid antibodies: Part I--Anticardiolipin and anti-β2-glycoprotein I antibodies

Over 30 years since it was first described as a discrete clinical entity, the antiphospholipid antibody syndrome (APS) remains a challenge for both laboratory workers and clinicians in a wide range of specialties. In addition to the presence of appropriate clinical features, the diagnosis of APS also fundamentally requires the finding of positive antiphospholipid antibody (aPL) test result(s), which comprise clot-based assays for the identification of lupus anticoagulant (LA) and immunologic ("solid-phase") assays such as anticardiolipin antibodies (aCL) and anti-β2-glycoprotein I antibodies (aβ2GPI). This article is the first of two that review the process for, and provides recommendations to improve, internal quality control (IQC) and external quality assurance (EQA; or proficiency testing) for aPL assays. These processes are critical for ensuring the quality of laboratory test results and thence the appropriate clinical diagnosis and management of APS. This article covers aCL and aβ2GPI testing. In brief, IQC is a process that helps control the quality of laboratory test results on a test-by-test basis; IQC should include samples that provide values around the assay critical cut-off values, and there is added value in the inclusion of non-kit assay controls. EQA is a process that helps laboratories assess their performance against those of their peers. For aCL and aβ2GPI testing, we provide some updated findings from the Royal College of Pathologists of Australasia Immunology Quality Assurance Program, and covering testing for the past 3 years (2009 to 2011 inclusive). Findings show similar trends to past years, indicating limited improvement in cross-laboratory test results and interpretations. In summary: (1) EQA participants reported greatly varying numerical test data for both aCL and aβ2GPI, with interlaboratory coefficients of variation > 50% with most test challenges; (2) there was considerable overlap in the interpretation (negative, positive, low positive, moderate positive, strong positive) that different participants ascribed to identical numerical test results; and (3) there was limited consensus among participants as to whether test results for individual EQA specimens were either positive or negative for aCL and/or aβ2GPI.

A comparison of Verotoxin B-subunit (Stx1B) and CD77 antibody to define germinal centre populations

We have directly compared the use of a CD77 antibody with the binding subunit of Shiga-like toxin 1, Verotoxin 1, and (Stx1B) for delineation on human tonsil cells. We determined that the Stx1B produced a greater intensity of staining than the CD77 antibody, allowing three sub-populations of germinal centre cells to be seen. The populations express high, medium, and low levels of globotriaosylceramide as determined by the binding of the Stx1B reagent. The strong staining patterns of Stx1B suggest that it may be useful in defining germinal center B cell populations.

Assessment of cell concentration and viability of isolated hepatocytes using flow cytometry

The assessment of cell concentration and viability of freshly isolated hepatocyte preparations has been traditionally performed using manual counting with a Neubauer counting chamber and staining for trypan blue exclusion. Despite the simple and rapid nature of this assessment, concerns about the accuracy of these methods exist. Simple flow cytometry techniques which determine cell concentration and viability are available yet surprisingly have not been extensively used or validated with isolated hepatocyte preparations. We therefore investigated the use of flow cytometry using TRUCOUNT Tubes and propidium iodide staining to measure cell concentration and viability of isolated rat hepatocytes in suspension. Analysis using TRUCOUNT Tubes provided more accurate and reproducible measurement of cell concentration than manual cell counting. Hepatocyte viability, assessed using propidium iodide, correlated more closely than did trypan blue exclusion with all indicators of hepatocyte integrity and function measured (lactate dehydrogenase leakage, cytochrome p450 content, cellular ATP concentration, ammonia and lactate removal, urea and albumin synthesis). We conclude that flow cytometry techniques can be used to measure cell concentration and viability of isolated hepatocyte preparations. The techniques are simple, rapid, and more accurate than manual cell counting and trypan blue staining and the results are not affected by protein-containing media.

FcgammaRIIb expression on human germinal center B lymphocytes

IgG antibody can specifically suppress the antibody response to antigen. This has been explained by the hypothesis that signaling through the B cell antigen receptor is negatively modulated by the co-ligation of immunoglobulin with the receptor for IgG, FcgammaRIIb. We hypothesized that inhibitory signaling through FcgammaRIIb would be counter-productive in germinal center cells undergoing selection by affinity maturation, since these cells are thought to receive a survival/proliferative signal by interacting with antigen displayed on follicular dendritic cells. We have identified and characterized a population of B lymphocytes with low/negative FcgammaRIIb expression that are present in human tonsil. Phenotypically these cells correspond to germinal center B cells and comprise both centroblast and centrocyte populations. In examining expression at the molecular level we determined that these B cells do not express detectable mRNA for FcgammaRIIb. We examined several culture conditions to induce expression of FcgammaRIIb on germinal center cells but could not determine conditions that altered expression. We then examined the functional consequence of cross-linking membrane immunoglobulin and the receptor for IgG on human B lymphocytes. Our results cast some doubt on the value of anti-IgG as a model for antigen-antibody complexes in studying human B cell regulation.

Clinical utility of the flow cytometric technique for shared rheumatoid epitope

The shared rheumatoid epitope (SRE) on the MHC class II antigen-presenting molecule constitutes a probable genetic risk factor for the occurrence of rheumatoid arthritis (RA) and may also determine disease severity. We have used a novel flow cytometric technique to determine the SRE in over 500 predominantly Caucasian patients attending a general rheumatology clinic. This technique has been validated against a polymerase chain reaction (PCR)/SSO molecular method. The SRE was observed in 90% of patients with Felty's syndrome (n = 10) and 75% of patients with RA (n = 178) as compared with 39% of patients with osteoarthritis or non-inflammatory rheumatic disorders (n = 73). Thus, the SRE determined by this method has a sensitivity for RA of 0.75, a specificity of 0.62 and an estimated positive predictive value of 0.02. In our RA cohort, there was no correlation between the functional outcome (health assessment questionnaire score) and SRE status. In conclusion, the determination of the SRE status by a flow cytometric method was found to have only modest sensitivity and specificity for RA; furthermore, the SRE did not correlate with functional outcomes. The clinical utility of the SRE assay is yet to be defined.

Analysis of the cord blood T lymphocyte response to superantigen

We have characterized the T lymphocyte population of the human neonate in respect of the expression of phenotypic profiles for naive, memory and differentiated populations. We have examined the response of the neonate T cell to the superantigen Staphylococcus enterotoxin B (SEB) and compared the response to T cells from healthy adults. We found that the primary response to SEB is equivalent in neonates and adults but that the secondary response demonstrates hyporesponsiveness in the neonate that is more profound than in adults. This response was associated with increased expression of CD25; the alpha chain of the IL-2 receptor, equivalent to that seen in responding cells from adults. A modest increased expression of CD122 and CD132, the beta and gamma chains of the IL-2 receptor, was also observed. There was no increase in the IL-4 receptor (CD124). The hyporesponsive neonate T cells proliferated in response to exogenous IL-2 but the response was less than none SEB treated cells. The neonate cells did not respond to IL-4. We also examined the expression of MHC class II molecules on SEB stimulated cells and found that both neonate and adult T cells upregulate MHC class II to a similar degree. The difference in the hyporesponsive cells appears to result in part from a lower production of IL-2 and in part from a lower ability of cord cells to respond to IL-2. Since the stimulated cord cells expressed IL-2 receptor at the same levels as similarly treated adult cells; there may be differences in down stream signaling pathways.

Interleukin 2 receptor regulation and IL-2 function in the human infant

IL-2 receptor is expressed at low levels on adult blood lymphocytes, and at lower levels on cord blood cells. IL-2 receptor alpha and beta chain expression increases gradually from 0-18 months of age. The level of soluble CD25 (IL-2 receptor alpha chain) has been reported to be elevated in cord blood. Quantitative RT-PCR showed that adult cells express 10 times as much CD25 mRNA as cord cells. Cord plasma showed only a marginal ability to strip CD25 from the membrane. To assess the functional consequences of low IL-2 receptor expression, cord and adult cells were activated in vitro. The response was stimulus-dependent, but cord cells upregulated CD25 readily. Cord and adult cells proliferated in an IL-2-dependent assay to a similar extent. Infants suffering acute infection showed marginally higher levels of membrane CD25 expression than infants without overt infection. Thus neonatal and infant lymphocytes express lower levels of IL-2 receptors than adult cells, reflecting lower mRNA concentrations at least for CD25; they are able to up-regulate receptors in response to in vitro stimulation and are able to respond in vitro to IL-2-dependent stimulation; however in vivo there may be a dampening down of the IL-2 system in infancy.