Eosinophils for the Emergency Physician
We’re all talking a good deal about the immune system these days. Explaining the difference between T cells and B cells to our parents, elaborating on the nuances of the cellular versus humoral response to our friends.
Most of the cell lines are getting a good rap. Thank goodness for adaptive immunity, we opine to whomever has the misfortune to get in our way.
But today’s column is (partly) about the forgotten cell in the bone marrow’s lineage. The Eosinophil. The poor cousin of immunity. Nobody’s getting on Fox news to rant about the role of eosinophils in human’s immune response to pathogens. So, let us redress the balance.
This cell only emerged from the cobwebs of my brain recently, when discussing a peculiar drug rash (aren’t they all) with a dermatologist, and she asked in a fevered shout and with uncharacteristic passion, ‘But what is the eosinophil count?’ Momentarily confused by the gravitas accorded to this single number, we got into talking about the role of eosinophils. Obviously, we were trying to work out whether this patient, who had been commenced on phenytoin a month ago and now had a morbilliform rash, had the diagnostic criteria for DRESS syndrome. Let’s get the educational component of the column out of the way. DRESS is a high mortality, bad dermatological condition. Standing for Drug Reaction with Eosinophilia and Systemic Symptoms, it is an idiosyncratic response to certain drugs – most commonly anticonvulsants and allopurinol – with a long latency (2-8 weeks), characterised by fever, lymphadenopathy, a widespread maculopapular spreading to vesicular and destructive rash, and any variety of multiorgan dysfunctions to failures. These people can get sick. There are many other immunological drug reactions which are in the differential diagnosis, but it is the eosinophilia which sets this one apart. Why the eosinophils particularly in this condition, I hear you ask? Are they part of the pathology, or part of the response?
Well the answer, the central premise of this article, is I don’t know. Neither did the dermatologist. So it requires a bit of a deep dive into the role of the eosinophil in general. You will all recall that eosinophils develop from myeloid precursors. They have bi-lobed nuclei and an absolute cornucopia of toxic mediators contained within, released on activation to fight both parasites (helminths in particular) and viruses. They do, however, kick own goals just as frequently, giving rise to a long list of destructive pathology of the auto-immune type. In health they are found in the circulation, and in the thymus, lymph nodes, and spleen. When things have turned bad, they infiltrate other organs: esophagus, skin, myocardium, and upper and lower airways. This deranged eosinophil function is a complex and poorly understood interaction between genetics and environmental influences. In DRESS syndrome, somewhere in the pathologic voyage is an abnormal adaptive T cell response, from CD4 to CD8 cells, dictated, in part, by the HLA antigen profile of the patient.
But enough! What use is this? We ER physicians, as we like to promulgate, are simple folk. An eosinophilia may simply be a useful data point in a few hen’s teeth situations: differentiating DRESS from other drug rashes, making us think of helminth infestations, directing us to think of esophagitis, asthma, rhinitis, polyangiitis (formerly Churg-Strauss), or myeloid neoplasms.
However, and you might guess where this is going, this piece on eosinophils was just a front. The word eosinophil is derived from both German and Greek, and means lover of acid, ostensibly for the way the cells take up stain under the microscope. And this took me nowhere but back to the beat poets. I spent many hours in your beautiful city of San Francisco wide-eyed among the shelves of the City Lights Bookstore, the home of Allen Ginsberg’s Howl, the shrine to the beat poets. I saw the best minds of my generation destroyed by madness, starving hysterical naked. I did, however, want to introduce you to an unknown Australian poet – hallucinatory, visionary, avant-garde, in the style of the beat poets – Benjamin Frater. My forearm is our unclear nuclear future/My forearm bleeds its own delight/My forearm refuses to bomb its enemies and dives into the rubble. He was incendiary and he soared high, sadly dead by twenty-eight, a victim of a medication mishap. Like many modern, brilliant poets, he was able to distil out truths, finding the philosophical heart of things to which we mortals are often blind. Bureaucracy has choked the great minds of this Decade/Aristocracy has made them poor/and religion fails a failing light … Long live the poets.