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The positive coreceptor function of complement receptor type 2 [CR2 (CD21)] on B cells is generally accepted, although its role in the enhancement of antibody production had only been proven in mice. The importance of this phenomenon prompted reinvestigation of the functional consequences of coclustering CD21 and the B cell receptor (BCR) on primary human cells. We found that, at non-stimulatory concentrations of anti-IgG/A/M, coclustering the BCR and CR2 enhanced the Ca2+ response, while activation marker expression, cytokine production, proliferation, and antibody production were all inhibited upon the coengagement of CR2 and BCR on human B cells. Thus, the “textbook dogma” claiming that C3d acts as an adjuvant to enhance humoral immunity is relevant only to mice and not to humans.

The complement system is a major humoral component of immunity and is essential for the fast elimination of pathogens invading the body. In addition to its indispensable role in innate immunity, the complement system is also involved in pathogen clearance during the effector phase of adaptive immunity. The fastest way of killing the invader is lysis by the membrane attack complex, which is formed by the terminal components of the complement cascade. Not all pathogens are lysed however and, if opsonized by a variety of molecules, they undergo phagocytosis and disposal inside immune cells. The most important complement-derived opsonins are C1q, the first component of the classical pathway, MBL, the initiator of the lectin pathway and C3-derived activation fragments, including C3b, iC3b and C3d, which all serve as ligands for their corresponding receptors. In this review, we discuss how complement receptors are utilized by various immune cells to tackle invading microbes, or by pathogens to evade host response.

Although many studies have been carried out on the psychometric aspects of computerized adaptive testing (CAT), its psychological aspects are less researched. Early studies claimed that CAT can be more motivating and induce less anxiety than traditional fixed-item tests (FIT). The purpose of this systematic review and meta-analysis was to gain a comprehensive understanding of the effects of CAT on motivation and anxiety in comparison to traditional fixed-item testing. Seven databases were examined. Articles were eligible if they employed an empirical study containing a direct comparison between CAT and FIT. Meta-analytical results showed no overall effect of test type on anxiety and motivation when comparing CAT with FIT ( k = 11, g+ = 0.06, p = .28). However, easier CAT had positive effect compared with FIT ( k = 2, g+ = .22, p < .001). Certain modifications in CAT administration can provide positive psychological effects for test-takers.

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