Microbial translocation has been proposed as the cause of systemic immune activation in chronic HIV-1 infection 
; however, it has not been extensively studied how these co-pathogens speed up deterioration of the immune response. DCs appear to be the common targets for HIV-1 invasion and translocation of other opportunistic pathogens at the mucosa. The functional compromise of DCs by HIV-1 infection is associated with immunosuppression and lack of control of microbial translocation. Given the pivotal roles of DCs in host immunity and viral pathogenesis, the interactions of DCs with HIV-1 have been preferentially targeted for exploiting the potential effects of opportunistic pathogens.
DCs treated with opportunistic pathogens, such as Malaria hemozoin
, Mycobacterium tuberculosis
, and C. albicans
, impairs degradative processing and MHC-II presentation of HIV-1 antigens to CD4+
T cells, and alters cytokine secretion, the enhanced DC-mediated viral trans
infection was also observed during certain opportunistic infections 
. In those published studies, the synthetic hemozoin
products, the M. tuberculosis
cell wall, or the heal-killed M. tuberculosis
or C. albicans
laboratory strains was used.
Here, the effects of P. marneffei on HIV-1-DC interactions were investigated. The difference is that the used P. marneffei and the C. albicans were directly isolated from AIDS patients. Our results demonstrated that both thermally dimorphic forms of P. marneffei activated DCs and promoted DC-mediated HIV-1 trans-infection of CD4+ T cells. Moreover, P. marneffei -stimulated DCs could further activate resting CD4+ T cells to induce more susceptible targets for HIV-1 infection. Our results have also shed light on the detailed mechanisms for the enhancement of viral spread. We demonstrated that heat-killed P. marneffei, along with C. albicans, promote viral uptake in MDDCs, altered viral intracellular sequestration, and importantly, facilitated MDDC-T cell contact by increasing ICAM-1 expression and efficiently concentrating HIV-1 particles in virological synapses.
DC activation and altered viral intracellular trafficking are associated with enhanced viral spread 
. Upregulation of HLA-DR, costimulatory molecules CD83 and CD86, and intercellular molecules on fungus-activated DCs, in general, would encourage DC-T cell conjugate formation. We and other groups have previously reported that increased ICAM-1 expression on DCs correlates with promoted viral transfer, due to stronger DC-T cell interactions through ICAM-1 binding to T-cell-expressed LFA-1 
. Fungus-stimulated DCs accelerate viral uptake and sequestrate intact viral particles in non-conventional, non-lysosomal tetraspanin CD81+
compartments. The harboring of intact virus into the non-classical multiple vesicular bodies might provide virus a means to escape from the cellular proteolysis 
. Upon encountering with CD4+
T cells, more viruses were recruited on the DC-T cell contacted sites. High levels of endocytosis and altered intracellular trafficking of HIV-1 appear to account for enhanced viral transmission mediated by fungus-activated DCs.
-stimulated DCs were less permissive for productive infection, which is consistent with previous reports of LPS and malaria hemozoin
. However, it remains to be clarified which fungal component(s) is responsible for HIV-1 restriction and the underlying mechanisms. LPS-matured DCs show dis-association of the susceptibility for HIV-1 infection with the capacity for mediating HIV-1 trans
. Post-entry restriction of HIV-1 infection in LPS-induced mature DCs has been noted, and inhibition on the levels of reverse transcription and post-integration have been further identified by using real time PCR quantification of viral DNA and integration 
. Reduced gene expression, such as for co-receptor CCR5, has been reported to be responsible for impaired productive infection of HIV-1 in malaria-hemozoin-
treated DCs 
. Higher levels of APOBEC3G and APOBEC3F (for “apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3G and 3F”) also have been shown to mediate the post-entry block of HIV replication in DCs and LPS can upregulate the expression of APOBEC3G/F 
. The antiretroviral protein, namely SAMHD1 (SAM domain HD domain-containing protein 1), has been recently identified to inhibit the early step of HIV-1 replication in dendritic- and myeloid cells 
. It might be possible that fungus-treated DCs increased the expression of these HIV-1 restriction factors and therefore become more resistant to HIV-1 infection.
DCs activate resting T cells and can provide more permissive targets for HIV-1 infection. We found that the stimulation of P. marneffe significantly accelerated DC-induced activation of resting CD4+ T cells, which indicates the pivotal importance of DC-driven T-cell activation for the high level of viremia and exacerbation of T-cell depletion in the late stage of HIV-1 infection. It would be interesting to confirm these in vitro observations in HIV-1-infected individuals.
Our findings revealed that DC function and its interaction with HIV-1 have been modulated by opportunistic pathogens for viral dissemination. Enhanced HIV-1 spread by DCs can target activated CD4+ T cells, which could further accelerate T-cell depletion and immunosuppression, leading to the lack of control of both viral and fungal pathogens. Our results highlight the importance of studying DC-HIV-1 interactions for understanding viral pathogenesis, and might provide a new insight into the interventions against HIV-1 infection and spread.