The afflictions suffered by immunocompromised individuals have historically been attributed to overt infections caused by bacterial and fungal pathogens. For this reason, treatment methods have focused on resolving these infections, with great success in terms of reducing short-term morbidity and mortality rates. This initial success only served to reinforce the dogmatic opinion that to ‘cure’ immunodeficiency, one needs only to resolve and prevent recurrence of bacterial and fungal infections. However, reports of long-term health problems in immunocompromised cohorts suggest that treatment of bacterial and fungal infections alone does not resolve all aspects of the disease, and that viruses may play a greater role than previously expected. This thesis investigates whether viral infections do indeed have a significant impact in the immunocompromised patient. The overall prevalence of blood-borne viral infections in immunocompromised cohorts was determined through the combined use of unbiased, metagenomic sequencing and qPCR. The viral species detected were compared with patient records in order to determine whether there were any correlations between viral presence and patient outcome following treatment. Furthermore, by investigating a cross-section of cohorts with both inherited and acquired immunodeficiences, commonalities and differences could be found in terms of the types of viruses that infect these cohorts and their abundance in patients with different types of immunodeficiency. The findings of this work suggest that a large number of clinically undiagnosed viruses infect immunocompromised patients, however the prevalence of these viruses varies according to the form of immunodeficiency and, to a lesser extent, according to differences between individuals in the same cohort. Importantly, some of the more common viruses detected appear to be correlated with poor patient outcomes such as graft rejection and future infectious complications. Overall, these results suggest that viral infections do indeed play a larger role in the health of immunocompromised patients than has previously been thought although whether this is due to a direct cause or as a consequence is yet to be determined.

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Anti-IgA Antikörper werden häufig als Ursache nicht-hämolytischer Transfusionsreaktionen angesehen. Die Inzidenz solcher Reaktionen schwankt zwischen 1:17.000 bis 1:770.000 und beruht größtenteils auf Fallberichten. Die Bedeutung dieser Antikörper, obwohl mit einer Prävalenz von 1: 18 bis 1:1.250 relativ häufig vorkommend, konnte in den circa vierzig Jahren seit ihrer Entdeckung nicht eindeutig geklärt werden; verschiedene Spezifitäten der Antikörper mit unterschiedlichen Reaktionen erschweren die Diagnose und eine klare Schematisierung. Ein Nachteil war bisher das Fehlen einer schnellen und unkomplizierten Nachweismethode, die in vielen Laboratorien angewandt werden kann. Die Ende der sechziger Jahre entwickelte Die Ende der 1960’er Jahre entwickelte Passive Hämagglutination (PHA) ist oft ungenau und unterliegt starken Schwankungen, kann aber relativ einfach durchgeführt werden und ist deshalb die Hauptmethode in der Diagnose von anti-IgA gewesen. Neuere und genauere Methoden wie Radio Immuno Assay (RIA) und Enzyme Linked Immunosorbent Assay (ELISA) sind weder schnell durchzuführen noch in vielen Laboratorien verfügbar. In dieser Arbeit wird eine neue Agglutinationsmethode, Particle Gel Immuno Assay (PaGIA) evaluiert und mit der PHA verglichen. Im ersten Teil wurden die Seren 105 gesunder Spender untersucht: 70 führten zu Reaktionen im PHA mit Titern bis 1:80 während keines im PaGIA reagierte, was die Spezifität des PaGIA unterlegt. Anschließend wurden elf Seren von Patienten mit selektivem IgA Mangel (sDIgA) und 23 Seren von Patienten mit variablem Immundefektsyndrom (CVID) auf das Vorliegen eines anti-IgA Antikörpers untersucht. Fünf Seren beider Patientengruppen führten in beiden Tests zu Agglutinationen und ein Serum (sDIgA) reagierte mit einem Titer von 1:1 in der PHA aber nicht im PaGIA. Die hier gefundenen Prävalenz (22% sDIgA, 45% CVID) und Größe der Titer (sDIgA>CVID) von anti-IgA stimmt mit den bisherigen Erkenntnissen überein. Weitere Untersuchungen konnten die Stabilität des PaGIA bzw. dessen Beads und Reproduzierbarkeit der Ergebnisse über mehrere Monate als auch die Möglichkeit subklassenspezifisches anti-IgA nachzuweisen darlegen. Der PaGIA stellt einen schnell und einfach durchzuführenden Test dar, mit dem anti-IgA Antikörper verschiedener Spezifität verläßlich bestimmt werden können, um Untersuchungen im großen Rahmen durchzuführen, die die Bedeutung der anti-IgA Antikörpern erhellen. / Anti-IgA antibodies are thought to be responsible for non-hemolytic transfusion reactions in one in 17,000 to one in 770,000 number of cases. This incidence is mainly supported by case reports. Despite their relative frequency of one in 18 to one in 1,250, since their discovery approximately forty years ago, the true significance of these antibodies has not yet been determined. Several specificities of these antibodies resulting in different reaction patterns make diagnosis and categorization difficult. Until recently, the lack of a fast and reliable laboratory test was a drawback. This test needed to be easily performed, fast, accurate, reproducible and accessible to many practitioners in many laboratories. The Passive Hemagglutination Assay (PHA), developed in the late 1960’s, is neither precise nor reliable but easy to perform and therefore has been the mainstay in diagnosis of anti-IgA. While newer methods, such as Radio Immuno Assay (RIA) and Enzyme Linked Immunosorbent Assay (ELISA), are neither fast nor easily performed but very precise. This thesis studies and evaluates a new agglutination assay, the Particle Gel Immuno Assay (PaGIA), and compares it to the PHA. In the first part of our study we established the specificity of PaGIA. Sera of 105 healthy blood donors were tested: 70 led to positive reactions with the PHA with titers up to 1:80 while none reacted with the PaGIA. Subsequently, eleven sera of patients with selective deficiency of IgA (sDIgA) and 23 sera of those with Common Variable Immunodeficiency (CVID) were tested for the presence of anti-IgA antibodies. Five sera in each group led to agglutinations in both assays and one serum reacted with a titer of 1:1 in the PHA but not in the PaGIA. The prevalence (22% sDIgA, 45% CVID) and strength of the titers (sDIgA>CVID) of anti-IgA corresponds with current knowledge. Further tests demonstrated the PaGIA’s and its beads stability and reproducibility over several months as well as the possibility for detection of subclass-specific anti-IgA. The PaGIA is a fast and easily performed assay which reliably detects anti-IgA antibodies of different specificities, thereby providing a tool for large scale studies to shed more light on the significance of anti-IgA antibodies.