This cohort of fatal influenza A(H1N1) infections confirms the presence of hemophagocytosis and HLH pathology. Moreover, the high percentage of HLH gene mutations suggests they are risk factors for mortality among individuals with influenza A(H1N1) infection.

cFollowing integration, HIV-1 in most cases produces active infection events; however, in some rare instances, latent infection events are established. The latter have major clinical implications, as latent infection allows the virus to persist despite antiretroviral therapy. Both the cellular factors and the viral elements that potentially determine whether HIV-1 establishes active or latent infection events remain largely elusive. We detail here the contribution of different long terminal repeat (LTR) sequences for the establishment of latent HIV-1 infection. Using a panel of full-length replication-competent virus constructs that reflect naturally occurring differences of HIV-1 subtype-specific LTRs and targeted LTR mutants, we found the primary ability of HIV-1 to establish latent infection in this system to be controlled by a four-nucleotide (nt) AP-1 element just upstream of the NF-B element in the viral promoter. Deletion of this AP-1 site mostly deprived HIV-1 of the ability to establish latent HIV-1 infection. Extension of this site to a 7-nt AP-1 sequence massively promoted latency establishment, suggesting that this promoter region represents a latency establishment element (LEE). Given that these minimal changes in a transcription factor binding site affect latency establishment to such large extent, our data support the notion that HIV-1 latency is a transcription factor restriction phenomenon.

Macrophage activation syndrome (MAS), typically presenting beyond the first year of life, is an often lethal cousin of familial hemophagocytic lymphohistiocytosis (fHLH). Defects in natural killer (NK) cell and CD8 T cell cytotoxicity result in a pro-inflammatory cytokine storm, cytopenia, coagulopathy, and multi-organ system dysfunction. MAS can occur in association with infections (herpes viruses), cancer (leukemia), immune deficient states (post-transplantation), and in autoimmune (systemic lupus erythematosus) and autoinflammatory conditions (systemic juvenile idiopathic arthritis). The distinction between fHLH, the result of homozygous defects in cytolytic pathway genes, and MAS is becoming blurred with the identification of single or multiple mutations in the same cytolytic pathway genes in patients with later onset MAS. Here, we review the literature and present novel cytolytic pathway gene mutations identified in children with MAS. We study the inhibitory effect of one these novel mutations on NK cell function to suggest a direct link between fHLH and MAS.

Gene transfer into primary human CD4 T lymphocytes is a critical tool in studying the mechanism of T cell-dependent immune responses and human immunodeficiency virus-1 (HIV-1) infection. Nucleofection® is an electroporation technique that allows efficient gene transfer into primary human CD4 T cells that are notoriously resistant to traditional electroporation. Despite its popularity in immunological research, careful characterization of its impact on the physiology of CD4 T cells has not been documented. Herein, using freshly-isolated primary human CD4 T cells, we examine the effects of Nucleofection® on CD4 T cell morphology, intracellular calcium levels, cell surface activation markers, and transcriptional activity. We find that immediately after Nucleofection®, CD4 T cells undergo dramatic morphological changes characterized by wrinkled and dilated plasma membranes before recovering 1 hour later. The intracellular calcium level also increases after Nucleofection®, peaking after 1 hour before recovering 8 hours post transfection. Moreover, Nucleofection® leads to increased expression of T cell activation markers, CD154 and CD69, for more than 24 hours, and enhances the activation effects of phytohemagglutinin (PHA) stimulation. In addition, transcriptional activity is increased in the first 24 hours after Nucleofection®, even in the absence of exogenous stimuli. Therefore, Nucleofection® significantly alters the activation state of primary human CD4 T cells. The effect of transferred gene products on CD4 T cell function by Nucleofection® should be assessed after sufficient resting time post transfection or analyzed in light of the activation caveats mentioned above.