ent features of apoptotic cells: (1) histologic eval-

uation of hematoxylin/eosin-stained tissue sections

revealed characteristic pyknotic nuclei and karyorrhexis,

(2) fluorescent terminal deoxynucleotidyl transferase

dUTP nick end labeling (TUNEL) staining demonstrated

systematic genomic degradation subsequent to poly

(ADP-ribose) polymerase activation, and (3) immuno-

histochemical staining identified the active form of the

executioner caspase, caspase-3. Light microscopy fur-

ther revealed massive loss of lymphocytes and disrup-

tion of germinal center architecture from the spleens of

septic patients compared with nonseptic controls. Sub-

sequent studies revealed that the cells that were depleted

during sepsis were CD4+ T cells, B cells, and follicu-

lar and interdigitating dendritic cells.20,21 Septic patients

were also found to have decreased circulating lympho-

cyte counts compared with nonseptic patients. Immune

cell apoptosis in septic patients has been demonstrated

in subsequent autopsy studies in both children and

neonates.22,23

7

Septic patients have a marked increase in apopto-

sis of circulating lymphocytes when compared with crit-

ically ill nonseptic patients.24 Apoptosis leads to lym-

phopenia that is persistent in septic patients, and the

degree of apoptosis is positively correlated with the

severity of sepsis and with poor outcome. Recent stud-

ies looking at immune cells from septic patients found

significant upregulation of the messenger RNA for the

septic-related etiologies.19

Autopsies

APOPTOTIC CELL DEATH IN SEPSIS

365

and were requiring vasopressors to

maintain an adequate arterial blood

pressure. The area of the liver that

demonstrated necrotic changes was the

region approximating the central vein.

This region is vulnerable to hypoxia

and decreased flow because of its

unique perfusion. Thus the hepatocyte

necrosis may have been secondary to

hypotension and hypoxia in the setting

of sepsis. Necrotic cell death was also

seen in the brain and heart of three

patients. However, these patients had

evidence of prior cerebrovascular inci-

dents or myocardial infarction.

Although these studies did not con-

clusively link sepsis to necrotic cell

Figure 31-2. Colonic epithelial apoptosis in a septic patient. Hematoxylin and eosin staining

death, there was unquestionable necro-

sis within

hypoxia-sensitive tissues.

of colonic epithelium of a septic patient (400× magnification). Arrows point to apoptotic cells

This necrosis could be explained by

being shed into the lumen of the colon. See Color Plate 36.

ischemia-reperfusion injury, as there is

well-documented microvascular patho-

proapoptotic genes Bid, Bim, and Bak and downregula-

logy in sepsis; however, the role of necrosis in sepsis

tion of BCL-2.25

remains poorly understood.

In addition to the hematopoietic compartment, the

gastrointestinal epithelium has long been a focus of

4. THE DEVELOPMENT OF CLINICALLY RELEVANT

study in sepsis research, and the gut has even been

referred to as the “motor” of the immune system.26 The

lining of the gastrointestinal tract “turns over” every 3

Early animal models of sepsis, on which previous re-

to 5 days and is a function of the balance between cell

search and therapies were based, involved lipo-

death and proliferation. Maintenance of this barrier is

(intravenous, intratracheal,

important in preventing translocation of live bacteria

or intraperitoneal).27 These models defined the classic

or bacterial toxins. The aforementioned autopsy study

proinflammatory phase of sepsis, characterized by

identified the increased incidence of colonic epithelial

tachycardia, tachypnea, hypotension, and high levels

apoptosis in both the villi and crypts in septic patients

systemic of TNF-α, IL-1, IL-6, and interferon (IFN)-γ,

compared with nonseptic patients (Figure 31-2).19 Apop-

and anti-inflammatory interventions in these models

tosis of epithelial cells was also seen in the ileum of septic

resulted in significant gains in survival. Unfortunately,

patients. Gastrointestinal epithelial apoptosis may lead

anti-inflammatory strategies based on these models

to breakdown of this important barrier, resulting in sys-

failed to provide significant mortality benefit to the

temic leakage of endogenous flora.

general septic population.1 Failure of these therapies

led to development of more clinically relevant models

3.2. Necrotic cell death in sepsis

of sepsis. The cecal-ligation and puncture (CLP) model

was developed to mimic sepsis owing to a ruptured

These autopsy studies also revealed necrotic cell death

appendix or bowel perforation.28 Pneumonia models

in other organ systems in patients who died with sep-

use bacteria commonly found to cause pneumonia,

sis.19 Microscopic evidence of necrosis in the liver was

such as Pseudomonas aeruginosa or Streptococcus pneu-

identified in approximately 33% of patients. Interest-

moniae.29 Pneumonia after CLP – or “two-hit” – models

ingly, apoptotic hepatocytes were seen in some patients

of sepsis mimic clinical scenarios involving secondary,

with identified necrosis, and the apoptosis occurred in

proximity to necrotic foci. It is important to note that

The identification of immune cell and gastrointesti-

almost all of the patients with sepsis were in septic shock

nal epithelial apoptosis in septic patients led researchers