Immunohistochemical characterization of phagocytic immune cell infiltration into different adipose tissue depots of dairy cows during early lactation

Abstract

The present study aimed to investigate whether phagocytic immune cells infiltrate into bovine adipose tissue (AT) and to study the effects of lactation and conjugated linoleic acid (CLA) supplementation on the invasion of phagocytic immune cells into different s.c. and visceral (v.c.) fat depots of primiparous dairy cows during the first 105 d in milk (DIM). German Holstein-Friesian cows (HF; n = 25) with a mean body condition score of 3.0 were divided into a control (CON) and a CLA group. From 1 DIM until sample collection, CLA cows were fed 100 g of CLA supplement/d (about 6% of c9,t11 and t10,c12 isomers each), whereas the CON cows received 100 g/d of a fatty acid mixture instead of CLA. The CON cows (n = 5 each) were slaughtered at 1, 42, and 105 DIM, and the CLA cows (n = 5 each) were slaughtered at 42 and 105 DIM. Adipose tissues (n = 150) from 3s.c. (tailhead, withers, and sternum) and 3 v.c. (omental, mesenteric, and retroperitoneal) depots were sampled. In addition, s.c. tailhead biopsies were collected by repeated surgical biopsies (3 samplings within 7 wk; n = 36) from 12 nonpregnant, nonlactating Simmental heifers (SM; mean body condition score = 5.0) fed diets of varying energy density to compare the changes in phagocytic immune cell infiltration with early lactating cows. Immunohistochemical analyses of different fat depots revealed a low incidence of phagocytic immune cell infiltration in early lactating cows. The portion of infiltrating macrophages (CD68+) in a few positive AT samples of HF cows was slightly lower in s.c. than v.c. fat and was positively correlated with both empty body weight and adipocyte size. However, no differences with regard to DIM and CLA supplementation were observed in HF cows. Increased accumulation of phagocytic immune cells, albeit at low cell numbers, in nonpregnant, over-conditioned SM heifers might be related to larger adipocytes secreting higher amounts of chemoattractant adipokines compared with the early lactating cows. In conclusion, the extent of fatness in HF cows may not be high enough to stimulate significant infiltration of phagocytic cells in AT and, therefore, these immune cells might have no major role in the immunologic and metabolic adaptations of AT during early lactation.

Invited review: Inflammation during the transition to lactation: New adventures with an old flame

“…It is not clear whether the periparturient cow has a similar 9 ability to counteract subacute inflammatory stressors. Combined with recent reports documenting the very limited quantity of immune cells found in the adipose tissue of lactating dairy cows (Akter et al, 2012), however, these findings have decreased our enthusiasm for an adipose-centric model of inflammation in transition cows. Perhaps it is not surprising that dairy cows, with a typical body fat content of ~20% at parturition , may not show the degree of adipose tissue inflammation observed in human obesity, where body fat can often exceed 40% (Kern et al, 2001;Cinti et al, 2005) for years.…”

Expression of NGF, BDNF and their receptors in subcutaneous adipose tissue of lactating cows

“…It is known that accumulation of fat could lead to a state of chronic mild inflammation (Ouchi et al, 2011), as demonstrated by granulocytic infiltration and cytokine secretion in AT (Osborn and Olefsky, 2012). An infiltration of macrophages into different AT depots was not observed after calving (Akter et al, 2012), but later in lactation, an infiltration of immune cells could occur.…”

Acute phase proteins in ruminants

“…Since obesity is not an issue in farm animals, inflammatory states of adipose tissue might not be relevant in ruminants used for meat and dairy production. Indeed, we have shown that macrophage infiltration in adipose tissue of dairy and beef cattle is virtually absent [153]. However, adipose tissue is mobilized in all mammals with the onset of lactation and the extraordinary milk yield from modern high performance dairy cows represents a biological extreme resulting in massive lipolysis that predisposes such cows to metabolic disease, compromised immune function and thus increased susceptibility towards infectious diseases [154].…”