Pathogenesis of macrophage activation syndrome and potential for cytokine- directed therapies

Histoplasmosis-Induced Hemophagocytic Syndrome: A Case Series and Review of the Literature

Background. Histoplasmosis-associated hemophagocytic lymphohistiocytosis (HLH) is a relatively rare disorder for which data are limited regarding optimal treatment and clinical outcomes in adults. We describe the clinical features, treatment, and outcomes of patients with histoplasmosis-associated HLH at our institution.

Methods. We performed a retrospective chart review of all inpatients at Parkland Hospital diagnosed with HLH associated with Histoplasma capsulatum from 2003 to 2013.

Results. Eleven cases of histoplasmosis-associated HLH over this time period were identified. Nine of eleven cases were males (82%). Nine of these patients had human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS), 1 was a renal transplant patient on immunosuppressants, and the other had no documented immunocompromise. The most common HLH criteria were splenomegaly (n = 10), fever (n = 10), and ferritin >500 ng/dL (n = 9). Urine Histoplasma antigen was positive in every patient tested (n = 9 of 9), and most antibodies for Histoplasma were positive if checked (n = 4 of 5). A majority of patients received liposomal amphotericin B (n = 9) with an average treatment duration of 11 days, and 5 patients also received prednisone, intravenous immunoglobulin (IVIG), or both. Overall, 5 patients died within 30 days (45.5%), and 7 patients died within 90 days (63.6%). Of the 5 patients that received immunosuppression, 4 died (80%), whereas in the group not given additional immunosuppression (n = 5), 2 died (40%).

Conclusions. Histoplasmosis-associated HLH among adults is a lethal disease of highly immunocompromised patients, especially patients with HIV/AIDS. Clinical features such as splenomegaly, elevated ferritin, and cytopenias should prompt evaluation for HLH in this population. Further data are needed to define the role of immunosuppression, IVIG, and highly active antiretroviral therapy in treating this condition.

Monogenic autoinflammatory diseases: Cytokinopathies

Rapid advances in genetics are providing unprecedented insight into functions of the innate immune system with identification of the mutations that cause monogenic autoinflammatory disease. Cytokine antagonism is profoundly effective in a subset of these conditions, particularly those associated with increased interleukin-1 (IL-1) activity, the inflammasomopathies. These include syndromes where the production of IL-1 is increased by mutation of innate immune sensors such as NLRP3, upstream signalling molecules such as PSTPIP1 and receptors or downstream signalling molecules, such as IL-1Ra. Another example of this is interferon (IFN) and the interferonopathies, with mutations in the sensors STING and MDA5, the upstream signalling regulator AP1S3, and a downstream inhibitor of IFN signalling, ISG15. We propose that this can be extended to cytokines such as IL-36, with mutations in IL-36Ra, and IL-10, with mutations in IL-10RA and IL-10RB, however mutations in sensors or upstream signalling molecules are yet to be described in these instances. Additionally, autoinflammatory diseases can be caused by multiple cytokines, for example with the activation of NF-κB/Rel, for which we propose the term Relopathies. This nosology is limited in that some cytokine pathways may be degenerate in their generation or execution, however provides insight into likely autoinflammatory disease candidates and the cytokines with which newly identified mutations may be associated, and therefore targeted.

An expanding role for interleukin-1 blockade from gout to cancer

There is an expanding role for interleukin (IL)-1 in diseases from gout to cancer. More than any other cytokine family, the IL-1 family is closely linked to innate inflammatory and immune responses. This linkage is because the cytoplasmic segment of all members of the IL-1 family of receptors contains a domain, which is highly homologous to the cytoplasmic domains of all toll-like receptors (TLRs). This domain, termed "toll IL-1 receptor (TIR) domain," signals as does the IL-1 receptors; therefore, inflammation due to the TLR and the IL-1 families is nearly the same. Fundamental responses such as the induction of cyclo-oxygenase type 2, increased surface expression of cellular adhesion molecules and increased gene expression of a broad number of inflammatory molecules characterizes IL-1 signal transduction as it does for TLR agonists. IL-1β is the most studied member of the IL-1 family because of its role in mediating autoinflammatory disease. However, a role for IL-1α in disease is being validated because of the availability of a neutralizing monoclonal antibody to human IL-1α. There are presently three approved therapies for blocking IL-1 activity. Anakinra is a recombinant form of the naturally occurring IL-1 receptor antagonist, which binds to the IL-1 receptor and prevents the binding of IL-1β as well as IL-1α. Rilonacept is a soluble decoy receptor that neutralizes primarily IL-1β but also IL-1α. Canakinumab is a human monoclonal antibody that neutralizes only IL-1β. Thus, a causal or significant contributing role can be established for IL-1β and IL-1α in human disease.