MAST CELL AND MYCOBACTERIUM LEPRAEIN EXPERIMENTAL LEPROSY

R. KUMAR *

M. C. VAIDYA **

ABSTRACT — The association of mast cells and lepra bacilli was studied in thefoot pad skin of immunosuppressed mice inoculated with 105 lepra bacilli. The mice werekilled at intervals varying from 2½ — 14 months postinoculation. M. leprae arefound in large numbers in nerves, blood vessels, muscle fibres, hair follicles, sweat andsebaceous glands. Mastocytosis and extensive degranulation are seen at similar sites.Since these are the structures most affected in leprosy where the lepra bacilli anddegranulating mast cells accumulate, there appears a close relationship between thetwo. This could be due to the composite role of mast cells in host tissue response andmastocytosis and degra-nulation may be related to this.

Key words: Experimental leprosy. Mycobacterium leprae. Mast cells.

1 INTRODUCTION

Mastocytosis and degranulation ofmast cells is a common feature reportedin a variety of conditions like allergy,bacterial infections, neoplasms and my-cobacterial diseases1,2,5,15. The mor-phology of the mast cell and its de-granulation usually depend upon thetype and severity of the disease. Thepresent study furthers our observationson the structural changes in the mastcells and their close association withlepra bacilli in the foot pad of the im-munosuppressed mouse inoculated withM. leprae.

2 MATERIAL AND METHODS

Immunosuppressed CBA mice (thy-mectomized and subjected to 900r total

((S

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boby irradiation) of both sexes, weigh-ing 20-25 gins, were employed through-out the experiments. They were ino-culated with freshly prepared suspen-sion of lepra bacilli (105) subcutane-ously into right foot pad. The animalswere killed at different intervals from2½ months to 14 months. The skinbiopsy was taken from the site of ino-culation. The biopsies fixed in Susasolution were embedded in paraffin tocut 5-7 µ. thick sections and stainedwith haematoxylin and eosin, ZiehlNeelsen, Fite Faraco technique for AFBand toluidine blue by standard method.

These techniques served to confirmthe diagnosis of the lesion produced inthe mouse foot pad to detect the pres-ence of bacilli and to reveal the mor-phology of the mast cells.

The normal mouse foot pad of same

strain served as control.

*) Lecturer, Department of Anatomy, All-India Institute of Medical Sciences, Ansari Nagar, New Delhi-110029, India.**) Professor of Anatomy, Cellular Immunology Laboratory, Department of Anatomy, All-India Institute of Medicalciences, Ansari Nagar, New Delhi-110029. India.

2 KUMAR, R. & VAIDYA, M.C. Mast cell and Mycobacterium leprae in experimental leprosy

3 OBSERVATIONS

Mastocytosis was observed irrespec-tive of the presence, absence or densityof the mycobacteria. The cells present-ed morphological changes in shape andsize, their affinity to accumulate aroundbacillary group, affected nerves, bloodvessels, muscles and skin appendages.In granulomas, the cells appeared lar-ger in size and the shape varied fromlong, thin to irregular (Fig. 1). Thedegranulating cells were seen in andaround the nerves, muscle fibre andneurovascular bundles (Figs. 3, 4). Thedegree of degranulation was observedto increase with the progress of lesion.The nerves with healthy axons did notshow much concentration of mast cellsaround them. There was an apparentincrease in the density of the mastcells as compared with the controlgroup and the cells showed massive de-granulation (Fig. 2). The degranulat-ing mast cells clustered around thethickened epineurium of the nerve bun-dle which was studded with bacilli(Figs. 5 and 6). The mast cells and thebacilli were seen in relation to thestructures, mostly involved in lesionsof leprosy. Besides the isolated mastcell granules and bacilli were also seenscattered in the dermis. Though themast cells and the bacilli had the pre-dilection for the same structures yet itwas not a constant feature to find bothof them together at the same site. Someaffected nerves showed thickened epi-neurium and after 13 months postino-culation, the bacilli were seen in groupsat this site (Fig. 6) . Mast cells werepresent both within and outside nervebundles in all the foot pads, many morein number in the one which showedbacilli.

4 DISCUSSION

Lymphocytes, plasma cells, macropha-ges and fibroblasts have been described

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to play essential immunological role inleprosy infection. There is, yet, anotherconnective tissue cell, the mast cell,which has been reported to be presentin abundance in the granulomas ofleprosy16. The mast cell has been clas-sified into different groups on the basisof its shape, size, staining tinctorialproperties and functional response tovarious agents. Its morphology variesfrom species to species and even indifferent tissues of same individual.The detailed morphology of mast cellwas conducted in normal mouse footpad in order to appreciate and comparethe changes observed in leprosy13. Themast cell of the normal (control) footpad showed round to oval shape andthe cells were conventionally recognizedby the presence of cytoplasmic metach-romatic granules masking the nucleus.Majority of the cells were intact andshowed perineural, perivascular, peri-glandular and perifollicular arrange-ment17.. Moreover occasional cell wasfound elongated in shape. The normalround shape of mast cell was confirmedby culturing the mast cell which whenmatured had smooth surface, roundednucleus which was masked by the cyto-plasmic granules. These cells werefound to be structurally and functio-nally same as the native cells 3,7,8,9

.

The majority of the mast cells showedaltered morphology in our experimentsand rarely a round cell was seen. Manyshapes and sizes of mast cells wereobserved in inoculated foot pad. It issuggested that the manifold types ofmast cells when encountered in thetissue, merely represented the variantof the same cell at different stages ofmaturity or activity and the structuraladaptations to surrounding tissues andStimuli18

..The structural and morpho-logical changes were also observed inmouse foot pad skin inoculated withserum obtained from lepromatous le-prosy patients14

.Thus this structuralresponse of mast cells could be caused

FI

FI

(*)

KUMAR, R. & VAIDYA, M.C. Mast cell and Mycobacterium leprae in experimental leprosy

GURE 1 - Photomicrograph of the skin of the mouse foot pad (immunosuppressed and inoculated withlepra bacilli) — The different shape and size of mast cells. Stain toluidine blue x 400. *

GURE 2 — Photomicrograph of the skin of the mouse foot pad (immunosuppressed and inoculatedwith lepra bacilli) — Degranulating mast cells. Stain toluidine blue x 400.

Mast cells (MCS).Degranulating mast cells (DMC).

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3

4 KUMAR, R. & VAIDYA, M.C. Mast cell and Mycobacterium leprae in experimental leprosy

FIGURE 3 - Photomicrograph of the skin of the mouse foot pad (immunosuppressed and inoculated withlepra bacilli) — Degranulating mast cells are seen in relation to muscle fibre. Stain toluidineblue x 400. *

FIGURE 4 - Photomicrograph of the skin of the mouse foot pad (immunosuppressed and inoculated withlepra bacilli) — Degranulating mast cells are seen in relation to neurovascular bundle. Staintoluidine blue x 400. *

(*) Muscle fibre (M). Nerve bundle (N). Blood vessel (BV).

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KUMAR, R. & VAIDYA, M.C. Mast cell and Mycobacterium leprae in experimental leprosy 5

FIGURE 5 — Photomicrograph of the skin of the mouse foot pad (immunosuppressed and inoculatedwith lepra bacilli) — Thickened epineurium studded with lepra bacilli. Stain Fite Faracox 400.

FIGURE 6 — Photomicrograph of the skin of the mouse foot pad (immunosuppressed and inoculatedwith lepra bacilli) — Degranulating mast cells around the lepra bacilli in thickenedepineurium. Stain toluidine blue x 400. *

(*) Nerve bundle (N). Lepra bacilli (LB). Epincurium (EPiN). Mast cells (MCS).

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6 KUMAR, R. & VAIDYA, M.C. Mast cell and Mycobacterium leprae in experimental leprosy

by either the infection or by the bacillidirectly. The morphological changes,mastocytosis and massive degranulationwas the response observed in all theexperimental groups which appeared tobe an integral part of the physiopatho-logy of this chronic infective process ofleprosy. This response was observedirrespective of the presence or absenceof the bacilli.

Abundance of eosinophils and mastcells have been reported in the granu-loma of tuberculoid leprosy16. Masto-cytosis has also been reported in murineand human leprosy 6,10,11,19, Increaseddensity and extensive degranulationwas a constant feature in our experi-ments where the cells were mainly seendegranulating around affected nerves,muscle fibres and blood vessels. Leprabacilli have been found in Schwanncells either as single or in clusters4,12,

14. They have the tendency to settle inthe nerves more than other structureswhich was clearly seen in our experi-ments. The isolated bacilli have alsobeen seen inside the muscle fibre andin relation to blood vessels. Similardistribution of the degranulating mast

cells was also observed in our study.This indicates the close association oflepra bacilli with the mast cells whicheither accumulated around the bacillior were lying in relation to the struct-ures severely affected in leprosy i.e.nerves, blood vessels, muscles, hair folli-cles and glandular elements4.

It is certain that mast cells do notcontribute to the formation of the gra-nulomabut appear to be definitely oneof the activated connective tissue cellsin them around the affected nerves,muscles and blood vessels. It is indeeddifficult to decide whether the observedmast cell changes are the cause or theresult of the morbid lesion in leprosy.The structural changes, mastocytosisand excessive degranulation of mastcells in the mouse foot pad of the mousein leprosy can be explained on the basisof defence mechanism against the inva-ding mycobacterium Their presencearound the group of Mycobacteriumleprae, is to be considered, if they areadvantageous to the host or to theorganism and this needs further inves-tigations.

RESUMO — A associação de mastócitos e bacilos de Hansen foi estudada na peledo coxim plantar de camundongos timectomizados e submetidos a 900r de radiação totalinoculados com 105 M. leprae. Os camundongos foram mortos em intervalos que variaramde 2 e meio a 14 meses após a inoculação. Bacilos foram encontrados em grande quanti-dade nos nervos, vasos sangüíneos, fibras musculares, folículos pilosos, glândulas sudorí-paras e sebáceas. Mastocitose e granulação extensa foram observadas nesses sítios. Jáque estas estruturas são as mais afetadas na hanseníase, nas quais os bacilos e osmastócitos granulosos se acumulam, parece haver uma estreita correlação entre osdois. Isto pode ser devido ao desempenho múltiplo dos mastócitos na resposta dostecidos hospedeiros; a mastocitose e a granulação podem estar relacionadas com essesfatos. Tradução do Editor.

Palavras chave: Hanseníase experimental. Mycobacterium leprae. Mastócitos.

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Received for publication in August 1981; accepted for publication in October, 1981.

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