Common variable immunodeficiency, immune thrombocytopenia, rituximab and splenectomy: important considerations.

Common variable immunodeficiency (CVID) is readily considered in patients presenting with recurrent sino-pulmonary infections, however this disease has a broad range of clinical manifestations and diagnosis can be delayed by several years. We present the case of a 44-year-old postpartum female who presented with nausea, vomiting and abdominal distension. Four years prior, she was hospitalized for treatment of immune thrombocytopenia (ITP) with splenectomy and rituximab followed by two episodes of bacterial meningitis despite immunizations. The recurrent meningitis had been attributed to splenectomy and immunotherapy. During this hospitalization, extensive workup for gastrointestinal pathology was negative and she was diagnosed with intestinal pseudo-obstruction. Her hospital course was complicated by development of severe pseudomonas pneumonia, and subsequent immunoglobulin testing and impaired antibody response to vaccines were consistent with CVID. We review the clinical presentation of CVID, its association with autoimmune disease, and treatment implications, specifically the impact of rituximab therapy and splenectomy on immunoglobulin function and risk of serious infection. Intestinal pseudo-obstruction has been reported in children with CVID, but literature search failed to reveal similar presentation in adults. Physicians must consider the heterogeneous clinical manifestations of CVID to avoid delay in diagnosis and treatment. Institution of appropriate therapy with immunoglobulin replacement is important to decrease risk of serious infection.

Atypical profiles and modulations of heme-enzymes catalyzed outcomes by low amounts of diverse additives suggest diffusible radicals' obligatory involvement in such redox reactions.

BACKGROUND: Peroxidations mediated by heme-enzymes have been traditionally studied under a single-site (heme distal pocket), non-sequential (ping-pong), two-substrates binding scheme of Michaelis-Menten paradigm. We had reported unusual modulations of peroxidase and P450 reaction outcomes and explained it invoking diffusible reactive species [Manoj, 2006; Manoj et al., 2010; Andrew et al., 2011, Parashar et al., 2014 & Venkatachalam et al., 2016]. METHODS: A systematic investigation of specific product formation rates was undertaken to probe the hypothesis that involvement of diffusible reactive species could explain undefined substrate specificities and maverick modulations (sponsored by additives) of heme-enzymes. RESULTS: When the rate of specific product formation was studied as a function of reactants' concentration or environmental conditions, we noted marked deviations from normal profiles. We report that heme-enzyme mediated peroxidations of various substrates are inhibited (or activated) by sub-equivalent concentrations of diverse redox-active additives and this is owing to multiple redox equilibriums in the milieu. At low enzyme and peroxide concentrations, the enzyme is seen to recycle via a one-electron (oxidase) cycle, which does not require the substrate to access the heme centre. Schemes are provided that explain the complex mechanistic cycle, kinetics & stoichiometry. CONCLUSION: It is not obligatory for an inhibitor or substrate to interact with the heme centre for influencing overall catalysis. Roles of diffusible reactive species explain catalytic outcomes at low enzyme and reactant concentrations. SIGNIFICANCE: The current work highlights the scope/importance of redox enzyme reactions that could occur "out of the active site" in biological or in situ systems.