Immune response to the hepatitis B vaccine among HIV-infected adults in Uganda.

BACKGROUND: Co-infection with hepatitis B virus (HBV) and human immunodeficiency virus (HIV) is common in sub-Saharan Africa (SSA) and can rapidly progress to cirrhosis and hepatocellular carcinoma. Recent data demonstrate ongoing HBV transmission among HIV-infected adults in SSA, suggesting that complications of HIV/HBV co-infection could be prevented with HBV vaccination. Because HBV vaccine efficacy is poorly understood among HIV-infected persons in SSA, we sought to characterize the humoral response to the HBV vaccine in HIV-seropositive Ugandan adults. METHODS: We enrolled HIV-infected adults in Kampala, Uganda without serologic evidence of prior HBV infection. Three HBV vaccine doses were administered at 0, 1 and 6 months. Anti-HBs levels were measured 4 weeks after the third vaccine dose. "Response" to vaccination was defined as anti-HBs levels ≥ 10 IU/L and "high response" as ≥ 100 IU/L. Regression analysis was used to determine predictors of response. RESULTS: Of 251 HIV-positive adults screened, 132 (53%) had no prior HBV infection or immunity and were enrolled. Most participants were women [89 (67%)]; median (IQR) age was 32 years (27-41), and 68 (52%) had received antiretroviral therapy (ART) for > 3 months. Median (IQR) CD4 count was 426 (261-583), and 64 (94%) of the 68 receiving ART had undetectable plasma HIV RNA. Overall, 117 (92%) participants seroconverted to the vaccine (anti-HBs ≥ 10 IU/L), with 109 (86%) participants having high-level response (anti-HBs ≥ 100 IU/L). In multivariate analysis, only baseline CD4 > 200 cells/mm3 was associated with response [OR = 6.97 (1.34-34.71), p = 0.02] and high-level response [OR = 4.25 (1.15-15.69)], p = 0.03]. CONCLUSION: HBV vaccination was effective in eliciting a protective humoral response, particularly among those with higher CD4 counts. Half of the screened patients did not have immunity to HBV infection, suggesting a large at-risk population for HBV infection among HIV-positive adults in Uganda. Our findings support including HBV vaccination as part of routine care among HIV-positive adults.

Single-file diffusion and neurotransmitter transporters: Hodgkin and Keynes model revisited.

Norepinephrine transporters (NETs) use the Na gradient to remove norepinephrine (NE) from the synaptic cleft of adrenergic neurons following NE release from the presynaptic terminal. By coupling NE to the inwardly directed Na gradient, it is possible to concentrate NE inside cells. This mechanism, which is referred to as co-transport or secondary transport (Läuger, 1991, Electrogenic Ion Pumps, Sinauer Associates) is apparently universal: Na coupled transport applies to serotonin transporters (SERTs), dopamine transporters (DATs), glutamate transporters, and many others, including transporters for osmolites, metabolites and substrates such as sugar. Recently we have shown that NETs and SERTs transport norepinephrine or serotonin as if Na and the transmitter permeated through an ion channel together 'Galli et al., 1998, PNAS 95, 13260-13265; Petersen and DeFelice, 1999, Nature Neurosci. 2, 605-610'. These data are paradoxical because it has been difficult to envisage how NE, for example, would couple to Na if these ions move passively through an open pore. An 'alternating access' model is usually evoked to explain coupling: in such models NE and Na bind to NET, which then undergoes a conformational change to release NE and Na on the inside. The empty transporter then turns outward to complete the cycle. Alternating-access models never afford access to an open channel. Rather, substrates and co-transported ions are occluded in the transporter and carried across the membrane. The coupling mechanism we propose is fundamentally different than the coupling mechanism evoked in the alternating access model. To explain coupling in co-transporters, we use a mechanism first evoked by 'Hodgkin and Keynes (1955) J. Physiol. 128, 61-88' to explain ion interactions in K-selective channels. In the Hodgkin and Keynes model, K ions move single-file through a long narrow pore. Their model accounted for the inward/outward flux ratio if they assumed that two K ions queue within the pore. We evoke a similar model for the co-transport of transmitter and Na. In our case, however, coupling occurs not only between like ions but also between unlike ions (i.e. the transmitter and Na ). We made a replica of the Hodgkin and Keynes mechanical model to test our ideas, and we extended the model with computer simulations using Monte Carlo methods. We also developed an analytic formula for Na coupled co-transport that is analogous to the single-file Ussing equation for channels. The model shows that stochastic diffusion through a long narrow pore can explain coupled transport. The length of the pore amplifies the Na gradient that drives co-transport.

Serotonin and norepinephrine transporters: possible relationship between oligomeric structure and channel modes of conduction.

In the past several years there has been significant progress made on the biophysics of neurotransmitter transporters, leading to the proposal of new models of substrate and ion permeation across membranes. Questions arising from these studies are as follows: How are substrate uptake and substrate-induced current related? Where and how does substrate-ion coupling occur? What is the functional significance of the coupled and uncoupled currents? Because of a long-standing interest and collaboration, and because of their importance for normal function and disease, the authors have focused on the properties of human norepinephrine and serotonin transporters, using other clones and mutations as specific needs arise. It has been know for decades that hNETs (human norepinephrine transporters) clear NE+ (norepinephrine) following its release in peripheral sympathetic and central noradrenergic synapses. Neuronal activity influences NE+ uptake, so one is also interested in the acute regulation of hNET. To study these problems, hNET-expressing cells have been developed that are suitable for patch clamp, radioligand uptake, biochemistry, and transiently expressed clones for structure-function analysis, and new protocols have been designed combining patch-clamp, microamperometry, Ca2+ imaging, and native catecholamine transporter preparations to study transporters in whole cells and isolated patches. Using these methods, Na-dependent, NE+-induced hNET currents that are blocked by cocaine and antidepressants, channel modes of NE+ conduction, voltage-dependent uptake coupled to NE+-induced ion channel activity, PKC (phosphokinase C) regulation of NE+ uptake, and transporter modulation by [Ca2+]i have all been discovered. There is also provocative new data on other transporters in this family, such as Li/Na mole fraction experiments in the Drosophila serotonin transporters and sided enkephalin block in proline transporters. These studies have led one to postulate the existence of a narrow pore within transporters through which the substrate (NE+ or serotonin, 5HT+) and other ions (principally Na+) pass. It is hypothesized that the pore resides in an oligomeric structure and that separate gene products of hNET or hSERT (human serotonin transporters) come together to form a channel.