SARS-CoV-2 infection and vaccination trigger long-lived B and CD4+ T lymphocytes with implications for booster strategies

BACKGROUNDImmunization against SARS-CoV-2, the causative agent of COVID-19, occurs via natural infection or vaccination. However, it is currently unknown how long infection- or vaccination-induced immunological memory will last.METHODSWe performed a longitudinal evaluation of immunological memory to SARS-CoV-2 up to 1 year after infection and following mRNA vaccination in naive individuals and individuals recovered from COVID-19 infection.RESULTSWe found that memory cells are still detectable 8 months after vaccination, while antibody levels decline significantly, especially in naive individuals. We also found that a booster injection is efficacious in reactivating immunological memory to spike protein in naive individuals, whereas it was ineffective in previously SARS-CoV-2–infected individuals. Finally, we observed a similar kinetics of decay of humoral and cellular immunity to SARS-CoV-2 up to 1 year following natural infection in a cohort of unvaccinated individuals.CONCLUSIONShort-term persistence of humoral immunity, together with the reduced neutralization capacity versus the currently prevailing SARS-CoV-2 variants, may account for reinfections and breakthrough infections. Long-lived memory B and CD4⁺ T cells may protect from severe disease development. In naive individuals, a booster dose restored optimal anti-spike immunity, whereas the needs for vaccinated individuals who have recovered from COVID-19 have yet to be defined.FUNDINGThis study was supported by funds to the Department of Experimental and Clinical Medicine, University of Florence (Project Excellence Departments 2018–2022), the University of Florence (project RICTD2122), the Italian Ministry of Health (COVID-2020-12371849), and the region of Tuscany (TagSARS CoV 2).     

Tridimensional ultrastructure and glycolipid pattern studies of Trypanosoma dionisii

Trypanosoma (Schizotrypanum) dionisii is a non-pathogenic bat trypanosome closely related to Trypanosoma cruzi, the etiological agent of Chaga's disease. Both kinetoplastids present similar morphological stages and are able to infect mammalian cells in culture. In the present study we examined 3D ultrastructure aspects of the two species by serial sectioning epimastigote and trypomastigote forms, and identified common carbohydrate epitopes expressed in T. dionisii, T. cruzi and Leishmania major. A major difference in 3D morphology was that T. dionisii epimastigote forms present larger multivesicular structures, restricted to the parasite posterior region. These structures could be related to T. cruzi reservosomes and are also rich in cruzipain, the major cysteine-proteinase of T. cruzi. We analyzed the reactivity of two monoclonal antibodies: MEST-1 directed to galactofuranose residues of glycolipids purified from Paracoccidioides brasiliensis, and BST-1 directed to glycolipids purified from T. cruzi epimastigotes. Both antibodies were reactive with T. dionisii epimastigotes by indirect immunofluorescense, but we noted differences in the location and intensity of the epitopes, when compared to T. cruzi. In summary, despite similar features in cellular structure and life cycle of T. dionisii and T. cruzi, we observed a unique morphological characteristic in T. dionisii that deserves to be explored.     

Operation of the voltage sensor of a human voltage- and Ca2+-activated K+ channel

Voltage sensor domains (VSDs) are structurally and functionally conserved protein modules that consist of four transmembrane segments (S1–S4) and confer voltage sensitivity to many ion channels. Depolarization is sensed by VSD-charged residues residing in the membrane field, inducing VSD activation that facilitates channel gating. S4 is typically thought to be the principal functional component of the VSD because it carries, in most channels, a large portion of the VSD gating charge. The VSDs of large-conductance, voltage- and Ca²⁺-activated K⁺ channels are peculiar in that more gating charge is carried by transmembrane segments other than S4. Considering its “decentralized” distribution of voltage-sensing residues, we probed the BK_Ca VSD for evidence of cooperativity between charge-carrying segments S2 and S4. We achieved this by optically tracking their activation by using voltage clamp fluorometry, in channels with intact voltage sensors and charge-neutralized mutants. The results from these experiments indicate that S2 and S4 possess distinct voltage dependence, but functionally interact, such that the effective valence of one segment is affected by charge neutralization in the other. Statistical-mechanical modeling of the experimental findings using allosteric interactions demonstrates two mechanisms (mechanical coupling and dynamic focusing of the membrane electric field) that are compatible with the observed cross-segment effects of charge neutralization.     

Reduced serum inhibition of platelet-activating factor activity in preeclampsia

We determined in normal nonpregnant (group 1) women, normal pregnant (group 2) women, and patients with preeclampsia (group 3) the serum inhibition of platelet-activating factor activity, the presence of detectable amounts of platelet-activating factor in the blood, and platelet responsiveness in vitro to platelet-activating factor, and to other agonists (adenosine diphosphate, collagen, and ristocetin), and prostacyclin (prostaglandin I2). In patients with preeclampsia (group 3) the serum inhibition of platelet-activating factor activity was significantly lower than that in groups 1 and 2. However, no detectable amounts of platelet-activating factor were observed. The mean values of platelet aggregation induced by platelet-activating factor, adenosine diphosphate, collagen and ristocetin, and the prostaglandin I2-inhibitory concentration of 50% which is inversely correlated with platelet sensitivity to prostaglandin I2, were not significantly different between groups 2 and 3. It is suggested that in preeclampsia the defect in serum inhibitory potential of platelet-activating factor--induced platelet aggregation may contribute to the disturbance in the homeostatic balance between proaggregant and antiaggregant substances.     

Bilirubin and uroporphyrinogen oxidation by induced cytochrome P4501A and cytochrome P4502B. Role of polyhalogenated biphenyls of different configuration

In previous work it was shown that hepatic microsomes from rats treated with 3-methylcholanthrene and similar inducers had increased bilirubin-degrading activity. The activity was further stimulated by addition of 3,4-tetrachlorobiphenyl (TCB), a response specifically dependent on CYP1A1. Here, we compared the effect of adding PCBs of either planar or non-planar configuration on rate of bilirubin degradation, monooxygenase activity and NADPH/O(2) consumption by liver microsomes from animals treated with either phenobarbital or 3-methylcholanthrene/beta-naphthoflavone. We also examined the oxidation of uroporphyrinogen (hexahydro-uroporphyrin) (URO'gen) under these conditions. Polychlorinated biphenyl (PCBs) stimulated the rate of bilirubin and URO'gen oxidation with microsomes expressing high levels of either CYP2B or CYP1A, inhibiting at the same time their monooxygenase activities (PROD and EROD, respectively); however, non-planar di-ortho-substituted PCBs were preferentially active with phenobarbitone-induced microsomes, in contrast to those active with 3-methylcholanthrene/beta-naphthoflavone microsomes, where a planar configuration was required for activity. An antibody raised against CYP2B1 markedly inhibited the PCB-dependent bilirubin degradation and PROD activities of phenobarbital-induced microsomes with similar dose-response curves for the two effects. Increased microsomal utilizations of NADPH and O(2) were also caused by PCBs with both types of induced microsomes and here again PCBs of different configuration were preferentially active. It is concluded that PCBs of the appropriate configuration may interact with either CYP1A1 or CYP2B1, increase production of oxidative species by an uncoupling mechanism, and lead to oxidation of target molecules in the cell, among these uroporphyrinogen and bilirubin.     

4-[6-(Dansylamino)hexylamino]-7-methyl-2-phenyl-1,8-naphthyridine as a new potential fluorescent probe for studying A1-adenosine receptor

A new fluorescent ligand for adenosine receptors, obtained by the insertion of a dansylamino-moiety with a linear hexyl spacer in the N4 position of a 1,8-naphthyridine adenosine receptor ligand, proved to possess a high affinity and selectivity for the A1 receptor subtype.