Bacterial killing by complement requires membrane attack complex formation via surface-bound C5 convertases.

The immune system kills bacteria by the formation of lytic membrane attack complexes (MACs), triggered when complement enzymes cleave C5. At present, it is not understood how the MAC perturbs the composite cell envelope of Gram-negative bacteria. Here, we show that the role of C5 convertase enzymes in MAC assembly extends beyond the cleavage of C5 into the MAC precursor C5b. Although purified MAC complexes generated from preassembled C5b6 perforate artificial lipid membranes and mammalian cells, these components lack bactericidal activity. In order to permeabilize both the bacterial outer and inner membrane and thus kill a bacterium, MACs need to be assembled locally by the C5 convertase enzymes. Our data indicate that C5b6 rapidly loses the capacity to form bactericidal pores; therefore, bacterial killing requires both in situ conversion of C5 and immediate insertion of C5b67 into the membrane. Using flow cytometry and atomic force microscopy, we show that local assembly of C5b6 at the bacterial surface is required for the efficient insertion of MAC pores into bacterial membranes. These studies provide basic molecular insights into MAC assembly and bacterial killing by the immune system.

Changes in laboratory results in transgender individuals on hormone therapy - a retrospective study and practical approach.

OBJECTIVE: Interpreting laboratory results for transgender individuals who started hormone therapy requires careful consideration, specifically for analytes that have sex-specific reference intervals. In literature, conflicting data exist on the effect of hormone therapy on laboratory parameters. By studying a large cohort, we aim to define what reference category (male or female) is most appropriate to use for the transgender population over the course of gender-affirming therapy. METHODS: A total of 2201 people (1178 transgender women and 1023 transgender men) were included in this study. We analyzed hemoglobin (Hb), hematocrit (Ht), alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), gamma-glutamyltransferase (GGT), creatinine, and prolactin, at three different time points: pretreatment, during hormone therapy, and after gonadectomy. RESULTS: For transgender women, Hb and Ht levels decrease after initiation of hormone therapy. The concentration of liver enzymes ALT, AST, and ALP decrease whereas the levels of GGT do not change statistically significantly. Creatinine levels decrease whereas prolactin levels rise in transgender women during gender-affirming therapy. For transgender men Hb and Ht values increase after starting hormone therapy. Liver enzymes and creatinine levels increase statistically significant as well upon hormone therapy while prolactin concentrations decrease. Overall, reference intervals in transgender people after 1 year on hormone therapy resembled those of their affirmed gender. CONCLUSIONS: Generating transgender-specific reference intervals is not essential to correctly interpret laboratory results. As a practical approach, we recommend to use the reference intervals of the affirmed gender from 1 year onwards after starting hormone therapy.