Placental macrophage (Hofbauer cell
) polarization is independent of maternal allergen-sensitization and presence of chorioamnionitis.
We have demonstrated that 9 weeks after initial maternal symptomatology and prolonged maternal viremia, the placenta still had detectable Zika virus present within stromal (Hofbauer) cells of the chorionic villi together with Hofbauer cell
Similar to placentas from infants with some congenital TORCH infections, placentas from second- and thirdtrimester infants with Zika virus infection demonstrate increased numbers of Hofbauer cells
within the stroma of chorionic villi.
The results also indicate that as in group 1, when in addition to hypervascularity other histologic features of diffuse preuterine placental hypoxia were present (delayed maturation, decreased extracellular matrix of chorionic villi, increased Hofbauer cells
, increased villous cytotrophoblasts), the frequency of clinical risk factors and abnormal outcomes is higher than that in pure chorangiosis (group 3), that is, placentas without the additional histologic findings mentioned in Figure 2 in which chorangiosis was most commonly focal.
In placentas of noncomplicated pregnancies, the Hofbauer cells
disappear or become scarce after the fourth to fifth month of gestation.
Based on RT-PCR, ISH and histopathology findings described in the study, CDC researchers concluded that Zika virus replicates in fetal brain and placental tissues and Hofbauer cells
may play an important role in the dissemination or transfer of Zika virus to the fetal brain.
(a) and (b) Placental histopathological results showing a rather loose villous stroma with numerous foamy/vacuolated Hofbauer cells
. Periodic Acid-Schiff (PAS) stain; original magnifications: x200 (a) and x1000 (b).
 demonstrated p24 antigen within scattered Hofbauer cells
but not within trophoblast cells or vascular endothelium, in 5/19 term placentas (26%) from HIV-positive women.
We directly localized Zika virus negative-sense replicative intermediates in Hofbauer cells
of placenta and neural cells and neurons by using ISH.
(24,57,64) When present, changes are mild and nonspecific and comprise chronic placentitis, with chronic villitis or increased Hofbauer cells
and patchy perivillous fibrin and mononuclear cells.
Microscopically, histiocytes were abundant in the maternal space (chronic intervillositis) and were noted within the fetal chorionic villi (Hofbauer cells
; Figure 1, panel A).
The knowledge that, as pregnancy advances, terminal villi and syncytial knots become numerous, villous cytotrophoblasts and Hofbauer cells
become less visible, the number of vascular profiles decrease, and the extracellular matrix of chorionic villi becomes denser, is of little help in individual cases, and the pathologist's experience is what matters.