Physiological and Pathological Variations in the Ultrastructure of Neutrophils and Monocytes

The human granulocyte nucleus: Unusual nuclear envelope and heterochromatin composition

The human blood granulocyte (neutrophil) is adapted to find and destroy infectious agents. The nucleus of the human neutrophil has a segmented appearance, consisting of a linear or branched array of three or four lobes. Adequate levels of lamin B receptor (LBR) are necessary for differentiation of the lobulated nucleus. The levels of other components of the nuclear envelope may also be important for nuclear shape determination. In the present study, immunostaining and immunoblotting procedures explored the levels of various components of the nuclear envelope and heterochromatin, comparing freshly isolated human neutrophils with granulocytic forms of HL-60 cells, a tissue culture model system. In comparison to granulocytic HL-60 cells, blood neutrophil nuclear envelopes contain low-to-negligible amounts of LBR, lamins A/C, B1 and B2, LAP2beta and emerin. Surprisingly, a "mitotic" chromosome marker, H3(S10)phos, is elevated in neutrophil nuclei, compared to granulocytic HL-60 cells. Furthermore, neutrophil nuclei appear to be more fragile to methanol fixation, than observed with granulocytic HL-60 cells. Thus, the human neutrophil nucleus appears to be highly specialized, possessing a paucity of nuclear envelope-stabilizing proteins. In consequence, the neutrophil nucleus appears to be very malleable, supporting rapid migration through tight tissue spaces.

The granulocyte nucleus and lamin B receptor: avoiding the ovoid

The major human blood granulocyte, the neutrophil, is an essential component of the innate immunity system, emigrating from blood vessels and migrating through tight tissue spaces to the site of bacterial or fungal infection where they kill and phagocytose invading microbes. Since the late nineteenth century, it has been recognized that the human neutrophil nucleus is distinctly not ovoid as in other cell types, but possesses a lobulated (segmented) shape. This deformable nucleus enhances rapid migration. Recent studies have demonstrated that lamin B receptor (LBR) is necessary for the non-ovoid shape. LBR is an integral membrane protein of the nuclear envelope. A single dominant mutation in humans leads to neutrophils with hypolobulated nuclei (Pelger-Huet anomaly); homozygosity leads to ovoid granulocyte nuclei. Interestingly, LBR is also an enzyme involved in cholesterol metabolism. Homozygosity for null mutations is frequently lethal and associated with severe skeletal deformities. In addition to the necessity for LBR, formation of the mature granulocyte nucleus also depends upon lamin composition and microtubule integrity. These observations are part of a larger question on the relationships between nuclear shape and cellular function.

Borrelia burgdorferi-induced ultrastructural alterations in human phagocytes: a clue to pathogenicity?

A chronic infection with the spirochaete Borrelia burgdorferi typically results in a multistage, multisystem illness. Thus, Lyme borreliosis may provide an interesting model to study the pathomechanisms of microbial persistence. In the present investigation, human peripheral blood monocytes, polymorphonuclear leukocytes, and synovial macrophages were incubated with B. burgdorferi and examined by light and electron microscopy. It was found that incubation with the spirochaetes induced distinct features in the phagocytes. Features which may be related to the pathogenesis of Lyme disease included the segmental uptake of spirochaetes with leaky lysosomes, the invagination of large membrane areas, the extra-lysosomal degradation of internalized B. burgdorferi cells and, finally, the formation of mononuclear syncytial cells and homotypic cell clusters. Features of unknown relevance were the occurrence of two types of cytoplasmic inclusion bodies and exocytic vesicles. These novel findings suggest that reactive alterations of the phagocytes may contribute to the pathogenesis of Lyme borreliosis, which could help to focus future histopathological studies. Moreover, these results may provide new insights into the pathogenesis of other infectious diseases characterized similarly by microbial persistence.

Effect of acute lead intoxication on the ultrastructure of neutrophils in the peripheral blood of the rat

The influence of lead acetate on the ultrastructure of peripheral neutrophils was investigated in adult male rats. It was found that a single intraperitoneal administration of lead at dose 150 mg Pb/kg b.w. led to ultrastructural changes in the neutrophils at 3 and 6 h post injection. At the time of testing the exposed population had a mean (+/- SD) blood lead concentration from 206.2 +/- 24.8 micrograms/100 ml to 75.2 +/- 9.9 micrograms/100 ml compared with a mean value of 4.0 +/- 0.7 micrograms/100 ml for the control groups. The ultrastructural alterations such as irregular nuclei with deep invaginations, plasma membrane pockets, the presence of vacuoles with a heterogeneous material and an increasing amount of RER cisternae, were most clearly expressed 6 h after lead administration. In addition there appeared sometimes nuclear pockets, and a prominent crystalline inclusion placed in the cytoplasmic matrix of some neutrophils. No differences in the mitochondrial morphology and cytoplasmic granule pattern between exposed and control rats were observed.